Are there words in English that include the prefix bi- whose current usage includes meanings other than 'two'?

To clarify, I am specifically looking for the prefix of Latin origin meaning "two". If we used the word bicycle (bi- + cycle) to refer to vehicles with one or three wheels, that would be an example of what I'm looking for.*

* Obviously we don't use bicycle this way; my example is to illustrate that if we did use bicycle this way, it would be the sort of thing I'm looking for.

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    Comments are not for extended discussion; this conversation has been moved to chat.
    – tchrist
    Commented Jun 25, 2018 at 13:05
  • 2
    Respectfully, I believe this question should be closed, as it is Off Topic for SE by virtue of being a List Question (as detailed here.)
    – Lumberjack
    Commented Jun 26, 2018 at 20:22
  • Actually we (as in the SE community) do use bicycle to mean vehicles powered by humans with cranks turning wheels, such as tricycles and unicycles. We're not alone in that.
    – Chris H
    Commented Jul 2, 2018 at 9:14
  • Are you specifically interested only in that particular prefix that means two, or would the di- of dilemma, originally meaning that choice between two but now not strictly restricted to only two options, count?
    – Jon Hanna
    Commented Jul 3, 2018 at 12:07

19 Answers 19


billion comes from bi- + million, as it originally meant the product of two millions - in other words, a million million. This usage persists in Europe (see long scale), but in America a billion means a thousand million. (In the long scale this would be called a milliard.)

See https://www.etymonline.com/word/billion

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – tchrist
    Commented Jul 2, 2018 at 1:07
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    I am not sure it’s true that a billion means a million million in Europe. Which European countries did you have in mind?
    – Simd
    Commented Jul 2, 2018 at 6:30
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    @Anush en.wikipedia.org/wiki/Long_and_short_scales "Countries where the long scale is currently used include most countries in continental Europe [..]"
    – DonFusili
    Commented Jul 2, 2018 at 11:48
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    @Anush like DonFusili said, but more specifically: «The traditional long scale is used by most Continental European countries and by most other countries whose languages derive from Continental Europe.» But the usage is getting progressively fuzzier, because of cultural contamination.
    – ANeves
    Commented Jul 2, 2018 at 15:35
  • In French for example, the obvious translation is milliard. Which word in current common use are you thinking of!
    – Simd
    Commented Jul 2, 2018 at 16:33

One is biscuit / biscotti, which literally means "twice cooked". Although the prefix here is "bis", it does start with "bi", so...

from Oxford Living Dictionary:


Middle English: from Old French bescuit, based on Latin bis ‘twice’ + coctus, past participle of coquere ‘to cook’ (so named because originally biscuits were cooked in a twofold process: first baked and then dried out in a slow oven so that they would keep).

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    I would think bis- would be an allomorphic variant of bi- in this case, due to ease of pronunciation. Commented Jun 22, 2018 at 13:47
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    @OliverMason It’s not. They’re separate prefixes. Bis in Latin is an adverb meaning ‘twice’, whereas bi- is simply the (historically regular) combining form of the numeral duō ‘two’. So one means ‘two’, the other means ‘twice’. Commented Jun 22, 2018 at 14:05
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    In the U.S., biscotti refers to a type of Italian cookie (U.K. biscuit) which actually is twice cooked. Commented Jun 22, 2018 at 15:19
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    Is the "Triscuit" thrice-cooked? Commented Jun 22, 2018 at 18:36
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    All sort of cookies are "biscotti" to us Italians.
    – Zachiel
    Commented Jun 23, 2018 at 16:38

The example given by the OP isn't too far off the mark. Rather than bicycle consider the shortened version "bike" where it may be used as part of another word e.g. quad-bike. In this case it is being used to describe a 4 wheeled cycle.


Might be a bit of a stretch, but...


a temporary encampment with few facilities, as used by soldiers, mountaineers, etc verb -acs, -acking or -acked (intr) to make such an encampment

Word Origin and History for bivouac

n. 1702, from French bivouac (17c.), ultimately from Swiss/Alsatian biwacht "night guard," from bei- "double, additional" + wacht "guard" (see wait (v.)). Original meaning was an army that stayed up on night watch; sense of "outdoor camp" is 1853. Not a common word in English before the Napoleonic Wars. Italian bivacco is from French. As a verb, 1809, "to post troops in the night;" meaning "camp out of doors" is from 1814.

I don't think it was ever used in the "double" sense in English, though.

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    Good lateral thinking, but etymologically not the bi- prefix, so I’m not sure if it really counts, though they have ended up looking the same in English. The bei- noted here is a common Germanic preposition (cognate with English by), which is unrelated to the Latin bi- prefix (from earlier *du̯i-, combining form of *du̯ō- ‘two’). Commented Jun 23, 2018 at 15:12
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    @Bahs Ah, I guess its more related to words that refer to "additional" or "supplementary" as in bypass, byproduct, or bylaw then.
    – Wolfgang
    Commented Jun 23, 2018 at 20:36
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    Precisely. It’s basically a ‘bywatch’. Commented Jun 23, 2018 at 20:37
  • Lovely! I never knew this! And in Middle English, the Germanic "be-" prefix (i.e. the one roughly analogous to, and with the same origin as, "be-" in standard German, as opposed to Greek "bi-" e.g. bewilder, befit, believe....), supposedly from was often written "bi-" by many authors, particularly Chaucer. So this is a very good example because exactly the same thing used to happen in English; I can't think of any "be-" words that keep the Chaucerian spelling in modern English. I bilieve (believe :) ) "Biforn" for "before" still exists in some dialects. Strictly speaking, the OP wanted ... Commented Jun 27, 2018 at 8:33
  • ... examples where "bi-" was the Greco-latin prefix, but +1 nonetheless! Commented Jun 27, 2018 at 8:34

While bigamy technically means the act of taking a second spouse while still legally married to a first (in cultures that enforce marital monogamy), in practice it also refers to people who have a whole series of such fraudulent marriages, a classic example being the sailor with a wife in every port. (The closely related word bigamist is the person who commits this act.)

The original meaning "two+spouse" has become "(two or more)+spouse". Not a huge change but a change nonetheless. A bicycle with three wheels is no longer a bicycle but a bigamist with three spouses is still a bigamist.

Dictionary cites:

  • bigamist (n.) "one who has had two or more wives or husbands at once," (Etymonline, emphasis added)

  • "A man was charged with bigamy for being married to 17 wives." (Sample usage from oxforddictionaries.com)

  • (noun) unlawful marriage, illegal marriage, multiple illegal marriages, multiple spouses, marrying multiple partners, marrying multiple wives, marrying multiple husbands (Burton's Legal Thesaurus, Android app, retrieved 2018-06-26, emphasis added.)

A web search for the term serial bigamist pulls up a fair number of newspaper articles about people with multiple concurrent fraudulent marriages. Grammatically the term doesn't make sense, unless the word refers to the pattern of deception and not the specific state of having exactly two spouses. (And note that I have not been able to find a reputable dictionary that covers this usage, but mainstream newspapers from multiple parts of the English-speaking world do use it.)

(Bigamy is distinct from polygamy, whether legal or not, where a man has multiple wives with the knowledge and relative consent of all parties. Rarer still is polyandry where one woman has multiple husbands, best known from impoverished areas where a set of brothers may share one farm and one wife. Both differ from modern polyamory where consenting adults create individualized rules about long term relationships.)

Newspaper usage:

  • Serial Bigamy

Serial bigamy is a lot more lucrative than it used to be. Immigrants looking for green cards will pay sham spouses thousands of dollars for an “I do,” said one law enforcement source [...] (New York Post, 2005-04-12)

  • Serial Bigamist

The downfall of a serial bigamist and conman (Irish Examiner headline, 2012-03-08)

Serial Bigamist Pleads Guilty (Toronto Sun video clip title, 2018-02-23)

  • Multiple Bigamist

Multiple Bigamist Leaves Court (BBC photo caption, 2009-07-27)

Bronx Multiple Bigamist: Woman Caught With Ten Marriages, Only Four Divorces (Headline, The Inquisitr, 2005-04-10 (Note: better known as a source of scandal and gossip than news))

  • Polyandry (There is a wealth of fascinating academic information about many patterns of polyandry online, but newspaper articles seem better for depicting language usage than technical papers, and they focus on the fraternal form):

Polyandry is still widely prevalent, a practice once common in Tibet. Brothers share a single wife, and it seems to create little domestic discord. (The Tribune (Chandigarh, North India) 2002-04-21)

They practice what is known as fraternal polyandry -- where the brothers of one family marry the same woman. Why? Tradition and economics. (CNN, 2008-10-24)

Definitions (all from dictionary.com) :

  • bigamy : noun (1) Law. the crime of marrying while one has a spouse still living, from whom no valid divorce has been effected.
  • polygamy : noun (1) the practice or condition of having more than one spouse, especially wife, at one time.
  • polyandry : noun (1) the practice or condition of having more than one husband at one time.
  • polyamory : noun (1) the practice or condition of participating simultaneously in more than one serious romantic or sexual relationship with the knowledge and consent of all partners.

My pet peeve: bimonthly, which means every 2 months, but also every 1/2 a month. The latter meeting your criteria.

Edit: I'm relieved that other people find this as odd as me. Yes bimonthly means twice a month and also every 2 months.


I suspect this happened because there aren't many things that occur every 2 months, so that usage fell out.

  • USA celebrated a bicentenary without confusion. No one suggests there should be another bicentenary in 8 years (ie, half a century later). Biennial plants have a two year life cycle, not a half year life cycle. No one mistakes a bicycle for something with half a wheel. It is disappointing that people have taken bimonthly / two-monthly / every two months to mean semi-monthly / twice monthly / every half month Commented Jul 2, 2018 at 11:51
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    I'd use fortnightly to describe something that happens every two weeks/twice a month, biweekly to describe something that happens twice a week, and bimonthly to describe something that happens every two months. It's not really intuitive, but the fact there's a unit of time meaning two weeks, which is roughly half a month, keeping in mind the biannual/biennial difference, relegates the ambiguity to intervals longer than two years. Commented Jul 2, 2018 at 16:40
  • Fortnight feels like British usage; it's rather rare in the US.
    – arp
    Commented Jul 7, 2018 at 1:55

If you can forgive the transformation of bi- to ba- over time, a barouche is a luxurious, four-wheeled carriage drawn by horses. The word ultimately comes from Latin birotus (bi- "two" + rotus "wheel").

See articles on the Online Etymology Dictionary and Wikipedia.

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    Took me a while to figure out the etymological meaning, until I remembered that the Romans had two-wheeled carriages.
    – Flater
    Commented Jun 25, 2018 at 9:52
  • @Flater, yes of course. I was thinking perhaps "rotus"might have referred to axles rather than individual wheels. Commented Jun 27, 2018 at 10:46
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    @WetSavannaAnimalakaRodVance: I initially thought the same, but then the "bi" would still really mean "two" since stagecoaches (as an example of 4 wheeled carriages) still have two axles today. But if you consider that carriages moved from 2 to 4 wheels without updating the name (quadrouche?), then the "two" in the name has become defunct and does fit with OP's question.
    – Flater
    Commented Jun 27, 2018 at 10:50

Perhaps bifurcation is an example? At least the mathematical sense given in Wiktionary,

The change in the qualitative or topological structure of a given family as decribed by bifurcation theory.

seems to allow for more general cases than a splitting in two. I’m afraid I don’t know enough about dynamical systems to be sure whether this is a possibility, and whether it would still be called bifurcation.

As @origimbo points out in the comments, a prominent example is the pitchfork bifurcation, "where the system transitions from one fixed point to three fixed points". This seems to be a clear example of what the OP is asking for.

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    In my experience, when I've seen the word "bifurcation" used to describe the behavior of some system, there is usually something splitting in two pieces. So I wouldn't count this as what the OP is looking for.
    – David Z
    Commented Jun 23, 2018 at 5:35
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    True story: I used to train engineers to maintain some equipment. Not all had English as their first language so we always checked they understood technical terms. On asking if everybody understood "bifurcated pipe" there were some blank looks, followed by the group comedian saying "yeah, it's a pipe that's been furcated twice". So a least one person thought "bifurcated" meant "split into three" (or maybe even four).
    – alephzero
    Commented Jun 23, 2018 at 10:06
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    In terms of dynamical systems with "but there are three of them!". The canonical example is probably the pitchfork bifurcation. To make things more confusing, this is often the first one a student is introduced to. en.wikipedia.org/wiki/Pitchfork_bifurcation
    – origimbo
    Commented Jun 24, 2018 at 19:39
  • @origimbo (+1) one could argue that the pitchfork bifurcation splits one stable fixed point into two stable fixed points (while also preserving the original fixed point as an unstable one). I am not sure but I suspect this is why they came to be called "bifurcations" in the first place. It's hard to tell because Poincare's original coining of the term is in French. But Hopf bifurcations, on the other hand, really seem to have no two-ness at all.
    – N. Virgo
    Commented Jun 26, 2018 at 6:20
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    Just had a quick look at that article. It's still splitting in two, not three. The third state is unstable and will stray, eventually oscillating between the two stable points. The two stable points are periodic attractors (in this case with a period of two), and the unstable point is a repulsor. Bifurcation is splitting in two. Trifurcation is splitting in three.
    – CJ Dennis
    Commented Jul 1, 2018 at 11:39

"Bicarbonate" and "bisulfate", maybe; these are (in chemistry) older, discouraged (but still in somewhat common use, especially "bicarbonate") names for the hydrogencarbonate and hydrogensulfate anions, respectively. The "bi" originally came from the observation that a hydrogencarbonate or hydrogensulfate salt has twice as much carbonate or sulfate per cation than a plain carbonate or sulfate salt.

"Bisexual" is at least a partial example; its original, narrow definition was "one who is sexually attracted to both males and females", but it now also has a broader definition as "one who is sexually attracted to persons of any gender" (thus allowing for persons with gender other than male or female).

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    Some would argue that one who is sexually attracted to persons of any gender is actually the definition of pansexual, but I'm just being picky here ;)
    – joH1
    Commented Jul 2, 2018 at 8:48
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    @joH1 yes, gay and straight people say rubbish like that all the time.
    – Jon Hanna
    Commented Jul 2, 2018 at 15:11
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    Incidentally, bisexual didn't originally mean "attracted to both males and females" but rather "internally hermaphrodite" (bisexual still means having both male and female organs in botany) in the 19th century theory that considered both gay and trans people as inverts. The word invert is no longer used that way because the theory was obviously a load of rubbish, albeit an historically important one in attempting to be biological rather than mythological, but bisexual remained in use because it still seemed applicable with the newer use of the terms heterosexual and homosexual.
    – Jon Hanna
    Commented Nov 19, 2018 at 11:20
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    Bisexual was the reason I asked this; I was tired of people (who aren't bi) saying bi people must be transphobic because of etymology. Commented Jul 25, 2022 at 7:23

Binary seems like a good fit for OP's conditions.

  1. Computers. binary code.
  2. Computers. an executable file stored in binary format.

The use of "binary" in computer science originally meant a stream of instructions entered as base-2 integers, 1 or 0, on or off. Think punch cards: hole or no hole. However, these days one would struggle to find any executable code written strictly in ones and zeros without examining the physical bits on optical or magnetic storage media.

Binary in modern computer science has a connotation of the opposite of plain text. FTP software offers a practical example of this opposition. Binary files are executable or data files largely composed of content that is not human readable. What makes this usage meet OP's guidelines is that binary files are usually examined not as a stream of base-2 integers, but of base-16 hexadecimals (0-9, A-F) in a hex editor. If you attempt to open a picture or video file in a text editor (such as Notepad within Windows), you'll quickly see that binary files consist of more than ones and zeros.

Addendum: In a subtly different context, the label of "binary" is applied to data comprised largely of extended characters (non-alphanumeric, non-punctuation). Consider base64 encoding of binary data. Within this context, coders do not consciously consider the base64 result to be binary, but something converted from binary. Whether the reader agrees that the binary label should be applied only to non-text data is not the point. All I'm saying is, there is precedent. There is prior art. This is happening to the English language heedless of anyone's approval.

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    "you'll quickly see that binary files consist of more than ones and zeros" Uh, no. They are presented to you as hexadecimal, but an hexadecimal digit is just four binary digits in a row, presented as one.
    – user89134
    Commented Jul 2, 2018 at 13:57
  • This is answer is completely incorrect. Binary means two-digit numeral system, always, never one, never 3 or more. This answer demonstrates complete ignorance of what binary means. It does not mean "computers". Commented Jul 4, 2018 at 14:43

I've several times heard the word bilingual used to mean "Spanish- and English-speaking," without regard to how many other languages a person may know. For example, a person who knows Spanish, English and French would still count as "bilingual" in this usage.

  • We need a bilingual secretary.

  • Are you bilingual?

In both cases, English-speaking is assumed, Spanish-speaking is implied, and the actual number of languages spoken is unimportant. No doubt this is more common in areas of the U.S. where there's a significant Spanish-speaking population.

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    I think bilingual still means knowing two languages, at least to me.
    – Simd
    Commented Jul 2, 2018 at 6:33
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    It seems to me that bilingual is used to mean "knowing the two languages that we care about in the context." In the case you stated, whether the person also knows French or Swahili really doesn't matter to the employer.
    – fool4jesus
    Commented Jul 2, 2018 at 15:18

Another potential contender can be bipolar

bipolar [adjective]

  • (of psychiatric illness) characterized by both manic and depressive episodes, or manic ones only.

  • (of a person) suffering from bipolar disorder.

source: ODO

From Royal College of Psychiatrists:

Bipolar I
If you have had at least one high or manic episode, which has lasted for longer than one week. You may only have manic episodes, although most people with Bipolar I also have periods of depression. Untreated, a manic episode will generally last 3 to 6 months. Depressive episodes last rather longer - 6 to 12 months without treatment.


Another possible word could be bicarbonate. Bicarbonate does not mean two carbonates, but rather hydrogenated carbonate. The carbonate ion is CO32-, while the bicarbonate ion is HCO3-

Wikipedia mentions this naming is rather outdated, and not really used in current chemistry:

The prefix "bi" in "bicarbonate" comes from an outdated naming system and is based on the observation that there is two times as much carbonate (CO3) in sodium bicarbonate (NaHCO3) and other bicarbonates as in sodium carbonate (Na2CO3) and other carbonates.


The definition given in Oxford Living Dictionaries seems to indicate that a biennale no longer has to be an event occurring every two years:

biennale, noun: A large art exhibition or music festival, especially one held biennially.

While maybe not as credible as a source of information, Wikipedia has this to say in its opening chapter on biennales:

... "Biennale" is therefore used as a general term for other recurrent international events (such as triennials, Documenta, Skulptur Projekte Münster).


Bisexual is gradually becoming an example as people realise that there is more than two genders.

From Merriam-Webster (emphasis mine):

bisexual [adjective]

1 a: (...)

b: of, relating to, or characterized by sexual or romantic attraction to members of both sexes; also : engaging in sexual activity with partners of more than one gender

  • I would say far from gradually as an endonym, where this is very much accepted, though some within the bisexual community prefer "both genders like one's own and genders unlike one's own" which is a binary definition but in covering two groups of genders rather than two genders is applying a binary grouping rather than pretending gender is binary.
    – Jon Hanna
    Commented Jul 2, 2018 at 15:02
  • (In etymology, sense b originates with the sense a you omitted and in the days of the theories of both trans and homosexual people as "inverts" described bisexual people as internally hermaphroditic. That's as discredited as the rest of the "invert" nonsense, but does have the legacy of leaving us with a word that biphobic people assume must mean bisexuals can't be attracted to non-binary people).
    – Jon Hanna
    Commented Jul 2, 2018 at 15:04
  • @JonHanna it is actually my distaste for that attempt to make the bi in bisexual mean 2 that led me to ask this question! Commented Jul 25, 2022 at 7:27

I think bipartisan may meet the OP's requirements.

However, this may be American-centric. Bipartisan certainly meant "two parties" originally. However, when someone says "bipartisan" here, they mean "broad political support" and are probably not consciously enumerating/counting parties. If there was a political option that enjoyed strong support between three political parties, would we say it has "tripartisan" support? I don't know - maybe an Anglophone from a multi-party country could opine.

  • In BrE we use the phrase "cross-party" instead, as we don't have (quite) as strong a two party system as the US.
    – AndyT
    Commented Jul 2, 2018 at 8:43

Balance is another common word that can be easily missed as the ancient prefix -bi is no longer discernible in the word. English borrowed it from French balance in the thirteenth century with the meaning "uncertainty, risk, hazard, doubt, wavering" and the meaning "weighing scales" came later. Today, it has many figurative and other senses not related to "two". It is originated from Latin bilanx meaning two-scaled.

The etymology of balance from OED:

< French balance (= Spanish balanza, Provençal balansa, Italian bilancia) < late Latin bilancia a pair of scales, < classical Latin bilanx, bilanc-em, adjective (in libra bilanx) ‘two-scaled,’ < bi- twice + lanx flat plate, scale.

Note: The French word balance might have been altered with false analogy from ballant (dangling, hanging) or ballare (to dance). The proper form is retained in the word bilan (balance-sheet) where French borrowed from Italian bilancio.


Shot in the dark here, but the first word that came to my mind that I use quite often myself but never fathomed was bistro.


I am not able to find proper roots for it, but for what I can make out it simply means "small restaurant / dining establishment" - in no relation to the meaning it originally held (two).

Though, bis- could very well be the root...


Some etymologies of "bismuth" suggest that the word originates from Arabic with "bi" coming from a word meaning "similar."

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