bathing costume vs swimming costume

bathing costume and swimming costume both are nouns.

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

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

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

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

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