Two of something

[david-us.livejournal.com]

Let's play a game!

I will make a list of words, in English, that convey the idea of two-of-something, or the state of two-ness, if you will. I would like to see a similar list like this in Russian. To the maxim extent possible, place the Russian word alongside the English word that comes closest to the same meaning, provided such an equivalent exists.

two
twice
double
second
duo
dual
bi- (as in biannual, bicycle, bilingual, binoculars, etc...)
couple
pair
twin
tandem

I can do the first one!

two - два  :)