dyad vs duo

dyad and duo both are nouns.

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

As nouns, dyad and duo are synonyms defined as:

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

dyad (noun)	duo (noun)
two items of the same kind	a musical composition for two performers
	a pair who associate with one another
	two performers or singers who perform together
	two items of the same kind