Not everybody in the Somerset side (4)

I believe the answer is:

some

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'not' is the definition.
Both the definition and answer are adverbs. Maybe there's a link between them I don't understand?

I cannot understand how the remainder of the clue works.

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(Other definitions for some that I've seen before include "Unknown or unspecified amount or number" , "certain" , "A little; not a little" , "Part" , "An unspecified quantity, not all" .)

I've seen this clue in the Evening Standard.

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