Knave (5)
I believe the answer is:
rogue
'knave' is the definition.
(I know that knave can be written as rogue)
This is all the clue.
(Other definitions for rogue that I've seen before include "Scamp" , "Dishonest chap; solitary (elephant)" , "Rapscallion" , "Dishonest man" , "A dishonest or unprincipled person" .)