duad vs twosome

duad and twosome both are nouns.

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

As nouns, duad and twosome are synonyms defined as:

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

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