Plough (4)
I believe the answer is:
till
'plough' is the definition.
(I know that plough is a more specific form of the action the till)
This is the entire clue.
(Other definitions for till that I've seen before include "Cash machine" , "cash container" , "To the time of the money drawer" , "Checkout - cultivate (land)" , "Work on farm" .)