It's poisonous and of proven ominousness (5)

I believe the answer is:

venom

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'it's poisonous' is the definition.
I can't tell whether this defines the answer.

'of proven ominousness' is the wordplay.
'of' says the answer is hidden in the clue.
'VENOM' can be found hidden inside 'proven ominousness'.

'and' acts as a link.

Can you help me to learn more?

(Other definitions for venom that I've seen before include "ill will" , "Virulence" , "Spite: toxin" , "Toxic substance" , "Virulent feeling" .)

I've seen this clue in the Evening Standard.

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