dyad vs twosome

dyad and twosome both are nouns.

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

As nouns, dyad and twosome are synonyms defined as:

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

dyad (noun)	twosome (noun)
two items of the same kind	a pair who associate with one another
	two items of the same kind