duo vs twosome

duo and twosome both are nouns.

Word	Noun	Adjective	Verb	Adverb
duo	Yes	No	No	No
twosome	Yes	No	No	No

As nouns, duo and twosome are synonyms defined as:

Other synonyms of duo include couple, duet.

As nouns, duo and twosome are synonyms defined as:

Other synonyms of duo include brace, couple, couplet, distich, duad, duet, dyad, pair, span, twain, yoke.

duo (noun)	twosome (noun)
a musical composition for two performers	a pair who associate with one another
a pair who associate with one another	two items of the same kind
two performers or singers who perform together
two items of the same kind