WordNet sense 1 (two items of the same kind):

brace, couplet, duet, duo, pair, span, twain, twosome, yoke, distich, duad, dyad

WordNet sense 2 (a pair of people who live together):

match, mates

WordNet sense 3 (form a pair or pairs):

pair off, partner off

WordNet sense 4 (make love):

mate, mate

WordNet sense 5 (link together):

couple on, couple up

WordNet sense 6 (bring two objects, ideas, or people together):

twin