pas de deux vs duet

pas de deux and duet both are nouns.

Word	Noun	Adjective	Verb	Adverb
pas de deux	Yes	No	No	No
duet	Yes	No	No	No

As nouns, pas de deux and duet are synonyms defined as:

pas de deux and duet: (ballet) a dance for two people (usually a ballerina and a danseur noble)

pas de deux (noun)	duet (noun)
(ballet) a dance for two people (usually a ballerina and a danseur noble)	(ballet) a dance for two people (usually a ballerina and a danseur noble)
	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