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Many English words use the prefixes uni-, bi-/di-, tri-, quad- and so on to mean one, two, three, and four. For example:

A unicycle has one wheel, a bicycle two, and a tricycle three.

I presume these prefixes are either of Greek or Latin origin, but from what little I know of these two languages, neither uses these prefixes as their numbers. That is, in Greek you wouldn't start counting by saying, Uni, di, tri, quad, ...

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4 Answers 4

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You are correct, they are from Latin and Greek, we have simply inherited terms from both. There is a good reference for Latin and Greek roots over at Wikipedia:

Uni meaning one:

un-, uni- one

  • language of origin: Latin

  • etymology: unus, unius

  • examples: unary, union

Bi/Di meaning two:

bi- two

  • language of origin: Latin

  • etymology: bis, "twice"; bini, "in twos"

  • examples: binoculars, bigamy, biscotti

di- two

  • language of origin: Greek

  • etymology: δι,

  • examples: dicot, dipole

Quadr meaning four:

quadr- four

  • language of origin: Latin

  • etymology: quattuor

  • examples: quadrangle, quadrillion

And so on; there are a lot of these and I'm no expert but believe that, although some of the roots from Latin and Greek essentially mean the same, there are some constraints on which ones to use in certain circumstances (see also: hypercorrection.) But don't quote me on that, though, I'll try and look a little information up.

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Here's a list of the PIE numerals, with cognates in major languages (including Latin and Greek). –  John Lawler May 8 '13 at 21:36
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It's true that in Latin there are words like "bis" ("twice") or "bini" ("in pairs") but the actual word "bi" is probably not a Latin word. "Two" in Latin is "duo". Taken separately, "bi" doesn't mean anything in Latin and is perhaps a borrowing from the early Basque language which isn't even Indo-European. "Bi", even in modern Basque, means "two". ("one, two, three, four, five" in Basque: "bat, bi, huru, lau, bost").

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As others have mentioned, the prefixes came from Latin (and Greek), and entered the widespread lexicon from the formal, scientific origins (primarily medicine and biology), where it was an established practice to use formal Latin in the naming and description of observed phenomena.

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They do come from both Latin and Greek as follows (along with the rest, up to ten):

uni comes from the Latin unus, meaning "one"
di comes from the Latin dis, meaning "twice" (originally from the Greek prefix di- meaning "two"
tri comes from the Latin tres (Greek treis), meaning three
quadra comes from the Latin quattour, meaning "four"
quinta/penta comes from the Latin quintus, meaning "fifth" and the Greek pente, meaning "five"
hexa comes from the Greek hex, meaning "six" (Latin is sex)
septa comes from the Latin septem, meaning "seven" (Greek is hepta) m
octa/o comes from the Latin octo (Greek okto), meaning "eight"
nona comes from the Latin nonus, meaning "ninth"
deca/deci comes from the Greek deka, meaning "ten" and from the Latin decimus, meaning "tenth"

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We also use penta- from Greek pente, meaning "five", and deci- from the Latin ordinal decimus (presumably by way of Greek). There are also (at least) two specialized words using Greek numbers rather than Latin: "tesseract", from tessera, meaning "four", and "enneagram" from ennea, "nine". –  Josh Caswell May 1 '11 at 5:19
@Josh thanks. Added in the common ones. –  snumpy May 2 '11 at 12:55
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