Deceive a man of conviction (3)
I believe the answer is:
con
'deceive' is the definition.
(I've seen this in another clue)
'a man of conviction' is the wordplay.
I cannot really see how this works, but
'man' could be 'n' (knight, a man in chess) and 'n' is present in the answer.
'of' could be 'o' and 'o' is found within the answer.
A single letter 'c' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for con that I've seen before include "Swindle or see" , "one in pen?" , "Direct steering; study" , "Rook" , "Opposed" .)