Pretty scrawny in a bathing suit (4)

I believe the answer is:

thin

I'm a little stuck... Click here to teach me more about this clue!

'pretty scrawny' is the definition.
'thin' can be an answer for 'scrawny' (similar in meaning). I'm unsure of the 'pretty' bit.

'in a bathing suit' is the wordplay.
'in' indicates the answer is hidden within the clue.
'THIN' is hidden within 'bathing suit'.

Can you help me to learn more?

(Other definitions for thin that I've seen before include "Lean; narrow" , "Lacking substance; not dense" , "Skinny" , "Flimsy" , "Superficial" .)

I've seen this clue in the Evening Standard.

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