sevens vs card game

sevens and card game both are nouns.

Word	Noun	Adjective	Verb	Adverb
sevens	Yes	No	No	No
card game	Yes	No	No	No

As nouns, card game is a hypernym of sevens; that is, card game is a word with a broader meaning than sevens:

sevens: a card game in which you play your sevens and other cards in sequence in the same suit as the sevens; you win if you are the first to use all your cards
card game: a game played with playing cards

Other hypernyms of sevens include cards.

sevens (noun)	card game (noun)
a card game in which you play your sevens and other cards in sequence in the same suit as the sevens; you win if you are the first to use all your cards	a game played with playing cards