Crossword Genius

One in a wet suit? (6)

Ross

I believe the answer is:

bather

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'suit?' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'one in a wet' is the wordplay.
'one' becomes 'the' (both can introduce a definite example of something).
'in' is an insertion indicator.
'a wet' becomes 'bar' (I can't justify this - if you can you should give a lot more credence to this answer).
'the' put within 'bar' is 'BATHER'.

Can you help me to learn more?

(Other definitions for bather that I've seen before include "man getting soaked?" , "one getting into the drink" , "One dipping in the briny?" , "Seaside swimmer" .)

I've seen this clue in the Evening Standard.
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