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' (common abbreviation for 'opus').
'for' says to put letters next to each other (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" .)