A very dirty look (4)

I believe the answer is:

perv

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'dirty look' is the definition.
The definition suggests a singular noun which matches the answer.

'a very' is the wordplay.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'very' becomes 'v' (common abbreviation).
'per'+'v'='PERV'

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(Other definitions for perv that I've seen before include "Kinks fan" , "behave lecherously"" .)

I've seen this clue in The Independent.

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