twosome vs couplet

twosome and couplet both are nouns.

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

As nouns, twosome and couplet are synonyms defined as:

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

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