WordNet (r) 3.0 (2006):

twosome
    n 1: two items of the same kind [syn: couple, pair,
         twosome, twain, brace, span, yoke, couplet,
         distich, duo, duet, dyad, duad]
    2: a pair who associate with one another; "the engaged couple";
       "an inseparable twosome" [syn: couple, twosome, duo,
       duet]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "twosome":
   both, bout, brace, contest, couple, couplet, decathlon, distich,
   double harness, double-header, doubles, doublet, duad, duet, duo,
   dyad, event, foursome, game, games of chance, go, match, mates,
   meet, pair, pentathlon, play, play-off, race, runoff, set of two,
   singles, span, sport, team, the two, threesome, twain, two, yoke