tank suit vs swimming costume

tank suit and swimming costume both are nouns.

Word	Noun	Adjective	Verb	Adverb
tank suit	Yes	No	No	No
swimming costume	Yes	No	No	No

As nouns, swimming costume is a hypernym of tank suit; that is, swimming costume is a word with a broader meaning than tank suit:

Other hypernyms of tank suit include bathing costume, bathing suit, swimsuit, swimwear.

tank suit (noun)	swimming costume (noun)
a woman's one-piece bathing suit	tight fitting garment worn for swimming