A man of conviction, in short (3)

I believe the answer is:

con

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'a man' is the definition.

I cannot understand how the rest of the clue works.

(Other definitions for con that I've seen before include "Study - swindle" , "do something?" , "Swindle; steer" , "Informally swindle" , "Not in favour" .)

I've seen this clue in the Evening Standard.

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