swimming costume vs bathing costume

swimming costume and bathing costume both are nouns.

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

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

swimming costume and bathing costume: tight fitting garment worn for swimming

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

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