couplet vs twosome

couplet and twosome both are nouns.

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

As nouns, couplet and twosome are synonyms defined as:

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

couplet (noun)	twosome (noun)
a stanza consisting of two successive lines of verse; usually rhymed	a pair who associate with one another
two items of the same kind	two items of the same kind