twosome vs doubleton

twosome and doubleton both are nouns.

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

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

twosome: 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

twosome (noun)	doubleton (noun)
a pair who associate with one another	(bridge) a pair of playing cards that are the only cards in their suit in the hand dealt to a player
two items of the same kind