Requite (6)
I believe the answer is:
avenge
'requite' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for avenge that I've seen before include "Geneva (anag)" , "Exact reparation for a wrong" , "eg Nave (anag.)" , "Redress, vindicate" , "Get one's own back for" .)