Not so much of it! (4)

I believe the answer is:

less

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'not so much' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for less that I've seen before include "Minus; not so much" , "minor" , "Comparative of 'a little'" , "So-called St James" , "Smaller in amout or degree" .)

I've seen this clue in the Evening Standard.

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