And certainly not greatly reduced (4,4)

I believe the answer is:

much less

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'and certainly not' is the definition.
I can't judge whether this defines the answer.

'greatly reduced' is the wordplay.
'greatly' becomes 'much' (I've seen this in another clue).
'reduced' becomes 'less' (a reduced amount).
'much'+'less'='MUCH LESS'

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