Slight advance traps knight (4)
I believe the answer is:
snub
'slight' is the definition.
(both can mean to treat someone disrespectfully)
'advance traps knight' is the wordplay.
'advance' becomes 'sub' (I've seen this in other clues).
'traps' indicates putting letters inside.
'knight' becomes 'N' (abbreviation for knight in chess).
'sub' enclosing 'n' is 'SNUB'.
(Other definitions for snub that I've seen before include "Cut; ignore" , "Rebuff humiliatingly" , "Ignore totally" , "Deliberate insult" , "Rude rejection" .)