Idiot missing half of proclamation in parliament (4)

I believe the answer is:

twit

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'idiot' is the definition.
(I've seen this in other clues)

I can't explain the rest of the clue.

(Other definitions for twit that I've seen before include "Stupid person" , "Slangily a foolish person" , "Silly person (colloq.)" , "Tease - fool" , "Ninny" .)

I've seen this clue in The Guardian.

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