Discontinue work for a doctor (4)
I believe the answer is:
drop
'discontinue' is the definition.
(dropping is a kind of discontinuing)
'work for a doctor' is the wordplay.
'work' becomes 'op' (short for opus).
'for' means one lot of letters go next to another (I've seen this in other clues).
'a doctor' becomes 'dr' (abbreviation).
'op' put after 'dr' is 'DROP'.
(Other definitions for drop that I've seen before include "Collapse, globule" , "Not a lot of water" , "Fall; delivery" , "Sweet; fall" , "Small amount of liquid" .)