Does anyone use "a beach" for "a bathing suit" or "bathing trunks"? I was leisurely looking at a thesaurus, and it showed "beach" synonymous to "bathing costume."

Thesauruses are not like dictionaries. They do not just supply synonms of words but also related vocabulary.

Beach does not mean those things.

By the way, in the UK we use 'swimming costume' and 'swimming trunks' for those items.
Never heard such usage.
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I might have been mistaken. The page of the dictionary may have indicated "beach costume," not just beach.

Thanks for your help.

Oh, that's interesting! So you don't use "swim suit" either? Just "costume"? (The way I look in a bathing suit, I'd like to have a swim DISGUISE!)
In the U.S. you can just say swim suit or swim trunks. The -ing on swim is optional.

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Then there's "Speedos" (a brand name of a swimming suit that has been generalized in the lexicon) and "bikini" for female swimmers and sun worshippers... Emotion: big smile