Gloomy medic touring department, heading off (5)
I believe the answer is:
drear
'gloomy' is the definition.
(I know that gloomy can be written as drear)
'medic touring department heading off' is the wordplay.
'medic' becomes 'dr' (doctor).
'touring' is an insertion indicator (tour can mean to go around).
'department' becomes 'area' (someone's department is their area of expertise).
'heading off' means to remove the first letter.
'area' with its first letter removed is 'rea'.
'dr' placed around 'rea' is 'DREAR'.
(Other definitions for drear that I've seen before include "grave" , "Dismal (literary)" , "Morose" , "Poetic dull and uninteresting" , "Gloomy and cheerless" .)