Male's been swimming without a costume (8)

I believe the answer is:

ensemble

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'costume' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

(Other definitions for ensemble that I've seen before include "Group of players; whole outfit" , "supporting cast" , "Company of players" , "Group of musicians or set of clothes" , "Performing group" .)

I've seen this clue in The Telegraph.

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