pair vs duet

pair and duet both are nouns.

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

As nouns, duet is a hyponym of pair; that is, duet is a word with a more specific, narrower meaning than pair:

Other hyponyms of pair include couple, duo, twosome, yoke.

As nouns, pair and duet are synonyms defined as:

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

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

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