bathing costume vs swimwear

bathing costume and swimwear both are nouns.

Word	Noun	Adjective	Verb	Adverb
bathing costume	Yes	No	No	No
swimwear	Yes	No	No	No

As nouns, bathing costume and swimwear are synonyms defined as:

Other synonyms of bathing costume include bathing suit, swimming costume, swimsuit.

bathing costume (noun)	swimwear (noun)
tight fitting garment worn for swimming	tight fitting garment worn for swimming