1. (n.) One and one; twice one.

2. (n.) The sum of one and one; the number next greater than one, and next less than three; two units or objects.

3. (n.) A symbol representing two units, as 2, II., or ii.

biform bifurcated bilateral bipartisan bipartite both brace couple couplet dichotomous distich double double harness doublet duad duadic dual dualistic duet duo duplex duplicated dyad dyadic identical match matched mates pair set of two span team the two twain twin twinned two-sided twosome yoke