A bit of a nitwit (4)

I believe the answer is:

twit

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'nitwit' is the definition.
(thesaurus)

I don't understand how the remainder of the clue works.

(Other definitions for twit that I've seen before include "Slangily a foolish person" , "Twerp" , "Silly person; tease" , "dunce" , "Taunt; fool" .)

I've seen this clue in the Evening Standard.

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