Doctor’s stand-in (5)
I believe the answer is:
locum
'doctor's stand-in' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for locum that I've seen before include "Stand-in, for a doctor say" , "Temporary replacement doctor" , "Person filling in" , "Physician's stand-in" , "Temporary deputy for doctor" .)