duad vs duo

duad and duo both are nouns.

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

As nouns, duad and duo are synonyms defined as:

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

duad (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