cards vs twenty-one

cards and twenty-one both are nouns.

Word	Noun	Adjective	Verb	Adverb
cards	Yes	No	No	No
twenty-one	Yes	Yes	No	No

As nouns, twenty-one is a hyponym of cards; that is, twenty-one is a word with a more specific, narrower meaning than cards:

cards: a game played with playing cards
twenty-one: a gambling game using cards; the object is to hold cards having a higher count than those dealt to the banker up to but not exceeding 21

cards (noun)	twenty-one (noun)
a game played with playing cards	a gambling game using cards; the object is to hold cards having a higher count than those dealt to the banker up to but not exceeding 21
	the cardinal number that is the sum of twenty and one

cards (adjective)	twenty-one (adjective)
	being one more than twenty