Crossword Genius

Stops before one gives utterance to (8)

Ross

I believe the answer is:

prevents

I'm a little stuck... Click here to teach me more about this clue!

'stops' is the definition.
(I've seen this before)

'before one gives utterance to' is the wordplay.
I cannot quite see how this works, but
'before' could be 'pre' (prefix meaning 'before') and 'pre' is found within the answer.
The remaining letters 'vents' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

(Other definitions for prevents that I've seen before include "Blocks" , "Stops from happening" , "Keeps form happening" .)

I've seen this clue in the Evening Standard.
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