swimming costume vs swimwear

swimming costume and swimwear both are nouns.

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

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

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

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