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, ...