Is there a prefix or adjective that means "one and a half", as "tri-" or "triple" is for "three"?

The exact usage I have is to describe "18" in terms of a dozen. Where I live they've started making 18-egg cartons, and the local grocer was wondering what name to give them in his computerised cash register, hoping for a single word.

Even slang, informal or invented term would do if there isn't such a term already.

  • I've wondered about this myself; in Russian there's полтора which is a very useful and common term. Your grocer should spearhead the initiative to create a new word :)
    – Turch
    Aug 23, 2013 at 15:23

7 Answers 7



However, it certainly isn't informal, and is also pretty obscure. About the only use of it is sesquicentennial and sesquipedalian which is at a few removes (it literally means 18inches long but it's originally figurative meaning of using long words is the only English meaning).

It certainly wouldn't go with dozen; one would just say "one and a half dozen", "dozen and a half" or "eighteen".


If you really want a word meaning 18 of something, you've got octodecuple, which has been used in mathematics at least as far back as 1816 and probably earlier. But really, don't; unless you're talking about properties of mathematical tuples where octodecuples are interesting in some particular way, it would just be horrible.

  • 5
    It is definitely obscure. If I asked at the market for a sesquidozen eggs, I'd more likely expect to receive a puzzled look than 18 eggs!
    – Ste
    Aug 19, 2013 at 14:16
  • 3
    @Ste and anyone who did get sesqui- might object to it being used with dozen.
    – Jon Hanna
    Aug 19, 2013 at 14:17
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    Absolutely. So we can conclude that it should be avoided at all costs, else we truly have egg on our faces.
    – Ste
    Aug 19, 2013 at 14:18
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    @Ste, there are running jokes in some nerdy/techie circles of deliberately coining such outrages, with e.g. microfortnight and nanocentury being used in some computing contexts due to such humour; but the humour is there precisely because they're clearly such bad ideas.
    – Jon Hanna
    Aug 19, 2013 at 14:21
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    the word 'dozen' derives from Latin as well but through old French. Hence if a neologism is invited 'sesqui-duodenary' as suggested would be better as both components of the word are directly derived from Latin
    – user49727
    Aug 19, 2013 at 22:20

One does occasionally hear the term three-halves.

An on-line search for three-halves yields many results, including

  • this image 3
    enter image description here
  • many references to Games of Three-halves, including Three-sided football 4, three types of 'football' played in Northern Ireland 5
  • a theatre performance 6
  • three-halves as a Superparticular number 7
  • and numerous other varied references.

The expression three-ha'-pence was in common usage in the UK until 1971 as a common way of expressing 1½d (one-and-a-half pence) in the pre-decimal currency system (1½d = 1/160th of a pound sterling £).

An English three-halfpence silver coin was minted around 1561-1582 during the reign of Elizabeth I. 8

British three-halfpence silver coins were produced for use in certain British colonies at various times during the reign of Queen Victoria (1819 - 1901)9, as illustrated 11: enter image description here

P.S. In answer to the original question, I would not suggest using the expression three half-dozens unless you want to test your readers / listeners!

  • Pictures always make an answer better :)
    – Timtech
    Aug 19, 2013 at 22:26

The prefix that means "times one and a half" is sesqui-, as in sesquicentennial for the 150th anniversary of something.

The OED includes the following terms that begin with sesqui-:

sesquialter, sesquialtera, sesquialteral, sesquialterate, sesquialterous, sesquibasic, sesquicentenary, sesquicentennial, sesquicompound, sesquiduple, sesquiduplicate, sesquinonal, sesquiocellus, sesquioctaval, sesquioxidation, sesquioxide, sesquioxidic, sesquioxidized, sesquipedal, sesquipedalian, sesquipedalianism, sesquipedality, sesquiplane, sesquiplicate, sesquiquadrate, sesquiquarta, sesquiquartal, sesquiquintile, sesquiseptimal, sesqui-square, sesquiterpene, sesquitertia, sesquitertial, sesquitertian, sesquitertious.

So it is hardly informal or slang; anything but, actually: it's rather a bit fancy.

  • I'd still say that sesquicentenary (and -ennial) and sesquipedalian would be the only that would see much use, and off those the last's etymological connection to "one and a half" isn't vital to understanding it.
    – Jon Hanna
    Aug 19, 2013 at 14:18
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    @JonHanna Those are the only ones I'm apt to use myself, that's for sure. Hm, given that the word duodecuple exists, I suppose one could justly derive sesquiduodecuple from it. But it won't win you friends in low places, that's for sure. There's probably some sort of octodecuple that would work better.
    – tchrist
    Aug 19, 2013 at 14:22
  • Especially since if you were really going to use sesquiduodecuple you could use the already-attested octodecuple. My answer hence updated to include that you could, and of course that you shouldn't!
    – Jon Hanna
    Aug 19, 2013 at 14:28
  • Ah, I see you edited that comment to consider octodecuple too, as I was replying.
    – Jon Hanna
    Aug 19, 2013 at 14:29
  • In mathematics we have sesquilinear, which, roughly speaking, is something linear in one variable and semilinear in the other..
    – GEdgar
    Aug 19, 2013 at 14:45

Another, rather archaic ordinal description is "half again as." That has the connotation of "half more" over one.

  • I like that this is a native English answer. “Dozen and half again (as many)” is more natural, but “half again a dozen” is fine too.
    – Jon Purdy
    Aug 20, 2013 at 7:19

Hendecasyllabic is derived from Greek for an 11 syllable word litterally meaning 11 sounds. The greek prefix for 18 would be octodeca- I wouldn't know how to form a noun from it. But here is a great resource on greek and latin numerical prefixes



This is my suggested neologism.

Both component words directly originate from their Latin counterparts:

sesqui- and duodenary


Where I come from, 18 is called "chai" from the two Hebrew letters that make up the word. Giving in multiples of 18 is considered good fortune as it's symbolic of giving life. I doubt, though, that you could refer to a dozen and a half eggs as a chai of eggs in a grocery without some perplexed looks, unless of course there are customers familiar with the term.

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