Poison of proven ominousness (5)

I believe the answer is:

venom

'poison' is the definition.
(venom is a kind of poison)

'of proven ominousness' is the wordplay.
'of' says the answer is hidden in the clue.
'VENOM' is hidden within 'proven ominousness'.

(Other definitions for venom that I've seen before include "Bitter malice" , "Poison - spite" , "Toxic substance" , "Virulence" , "Virulent feeling" .)

I've seen this clue in the Evening Standard.

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