Teetotal surgeon in a hospital department carrying can (9)
I believe the answer is:
abstinent
'teetotal' is the definition.
(synonyms)
'surgeon in a hospital department carrying can' is the wordplay.
'surgeon' becomes 'bs' (Bachelor of Surgery).
'in' is an insertion indicator.
'hospital department' becomes 'ENT' (abbreviation for Ear, Nose and Throat department).
'carrying' means one lot of letters goes inside another.
'can' becomes 'tin' (both are metal containers).
'a'+'ent'='aent'
'bs' placed within 'aent' is 'absent'.
'absent' going around 'tin' is 'ABSTINENT'.
(Other definitions for abstinent that I've seen before include "Avoiding port, perhaps" , "Refraining from drinking alcohol" , "Forsaking alcohol" , "Not indulging appetite for food or drink" , "Going without, especially food and alcohol" .)