duo vs pair

duo and pair both are nouns.

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

As nouns, pair is a hypernym of duo; that is, pair is a word with a broader meaning than duo:

As nouns, duo and pair are synonyms defined as:

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

duo (noun)	pair (noun)
a musical composition for two performers	two people considered as a unit
a pair who associate with one another	a set of two similar things considered as a unit
two performers or singers who perform together	a poker hand with 2 cards of the same value
two items of the same kind	two items of the same kind

duo (verb)	pair (verb)
	engage in sexual intercourse
	bring two objects, ideas, or people together
	arrange in pairs
	occur in pairs
	form a pair or pairs