doubleton vs duet

doubleton and duet both are nouns.

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

As nouns, duet is a hypernym of doubleton; that is, duet is a word with a broader meaning than doubleton:

doubleton: (bridge) a pair of playing cards that are the only cards in their suit in the hand dealt to a player
duet: two items of the same kind

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

doubleton (noun)	duet (noun)
(bridge) a pair of playing cards that are the only cards in their suit in the hand dealt to a player	(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