Increase overwhelming working doctor (7)
I believe the answer is:
surgeon
'doctor' is the definition.
(surgeon is a type of doctor)
'increase overwhelming working' is the wordplay.
'increase' becomes 'surge' (surge is a kind of increase).
'overwhelming' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'working' becomes 'on' (on can mean working or activated).
'surge'+'on'='SURGEON'
(Other definitions for surgeon that I've seen before include "Medical knife wielder" , "Doctor with a scalpel" , "Go, nurse for the operator" , "Operating medical practitioner" , "Medical specialist" .)