Cheat a man of conviction (3)

I believe the answer is:

con

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'cheat' is the definition.
(con is a kind of cheat)

I don't understand how the rest of the clue works.

(Other definitions for con that I've seen before include "Scam, swindle" , "do something?" , "Defraud" , "Direct steering; study" , "Opposed" .)

I've seen this clue in the Evening Standard.

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