From WordNet (r) 3.0 (2006):
duo
n 1: two items of the same kind [syn: couple, pair,
twosome, twain, brace, span, yoke, couplet,
distich, duo, duet, dyad, duad]
2: two performers or singers who perform together [syn: duet,
duette, duo]
3: a pair who associate with one another; "the engaged couple";
"an inseparable twosome" [syn: couple, twosome, duo,
duet]
4: a musical composition for two performers [syn: duet,
duette, duo]