couple vs twosome

couple and twosome both are nouns.

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

As nouns, couple and twosome are synonyms defined as:

Other synonyms of couple include duet, duo.

As nouns, couple and twosome are synonyms defined as:

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

couple (noun)	twosome (noun)
a pair who associate with one another	a pair who associate with one another
a pair of people who live together	two items of the same kind
(physics) something joined by two equal and opposite forces that act along parallel lines
two items of the same kind
a small indefinite number

couple (verb)	twosome (verb)
engage in sexual intercourse
link together
bring two objects, ideas, or people together
form a pair or pairs