Not good (3)

I think it could be either:

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2-2

bad

'not good' is the definition.
(bad is the opposite of good)

This is all the clue.

(Other definitions for bad that I've seen before include "Of poor quality" , "Substandard" , "Rotten, evil" , "Severe; of low standard" , "SECOND HALF OF 16" .)

I've seen this clue in The Mirror, the Evening Standard and the Universal.

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