card game vs twenty-one

card game and twenty-one both are nouns.

Word	Noun	Adjective	Verb	Adverb
card game	Yes	No	No	No
twenty-one	Yes	Yes	No	No

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

card game: 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

card game (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

card game (adjective)	twenty-one (adjective)
	being one more than twenty