Revoke (a law) (6)
I believe the answer is:
'revoke a law' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for repeal that I've seen before include "Revoke, a law say" , "This is what O'Connell wanted" , "Annul an act of parliament" , "set aside" , "reverse" .)