He contradicts a gentleman (3)
I believe the answer is:
cad
'he' is the definition.
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for cad that I've seen before include "A rotten chap, no integrity" , "Rogue" , "Dishonourable man of decadent sort" , "A knave, real rotter" , "One behaves dishonourably" .)