swimming costume vs bathing suit

swimming costume and bathing suit both are nouns.

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

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

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

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

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