swimwear vs tank suit

swimwear and tank suit both are nouns.

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

As nouns, tank suit is a hyponym of swimwear; that is, tank suit is a word with a more specific, narrower meaning than swimwear:

Other hyponyms of swimwear include bikini, two-piece, maillot, bathing trunks, swimming trunks.

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