Cut the grass (3)
I believe the answer is:
mow
'cut the grass' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for mow that I've seen before include "Scythe" , "Cut grass or grain" , "'Cut, grass say (3)'" , "Cut (e.g. grass)" , "'Cut down, hay, say (3)'" .)