rummy vs cards

rummy and cards both are nouns.

Word	Noun	Adjective	Verb	Adverb
rummy	Yes	Yes	No	No
cards	Yes	No	No	No

As nouns, cards is a hypernym of rummy; that is, cards is a word with a broader meaning than rummy:

rummy: a card game based on collecting sets and sequences; the winner is the first to meld all their cards
cards: a game played with playing cards

Other hypernyms of rummy include card game.

rummy (noun)	cards (noun)
a card game based on collecting sets and sequences; the winner is the first to meld all their cards	a game played with playing cards
a chronic drinker

rummy (adjective)	cards (adjective)
beyond or deviating from the usual or expected