A proverb; a cutter (3)
I believe the answer is:
saw
I believe this clue is a double definition.
'a proverb' is the first definition.
(I know that proverb can be written as saw)
'a cutter' is the second definition.
(I know that saws cut things)
(Other definitions for saw that I've seen before include "Cutting tool or maxim" , "Witnessed" , "A maxim with teeth" , "Cutting tool or old saying" , "Picked out" .)