Hack (off) (3)
I believe the answer is:
lop
'hack off' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for lop that I've seen before include "Remove branches from a tree" , "Chop (off)" , "Cut away branches or twigs" , "Cut (e.g. branch off)" , "Prune, cut the top off" .)