Sound excessively thick-headed (4)

I believe the answer is:

toot

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'sound' is the definition.
(tooting is a kind of sounding)

'excessively thick-headed' is the wordplay.
'excessively' becomes 'too' (synonyms).
'thick-headed' becomes 't' (this could be a standard abbreviation which I don't know about).
'too'+'t'='TOOT'

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(Other definitions for toot that I've seen before include "Brief blast on a horn" , "Sound one's horn" , "Noise made by car horn" , "Do it on a flute" , "Briefly blow" .)

I've seen this clue in the Evening Standard.

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