duad vs doubleton

duad and doubleton both are nouns.

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

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

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

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