tank suit vs bathing suit

tank suit and bathing suit both are nouns.

Word	Noun	Adjective	Verb	Adverb
tank suit	Yes	No	No	No
bathing suit	Yes	No	No	No

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

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

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