Gloomy doctor close to losing head (5)
I believe the answer is:
drear
'gloomy' is the definition.
(I've seen this in another clue)
'doctor close to losing head' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'close to' becomes 'near' (close to means nearby).
'losing head' means to remove the first letter.
'near' with its initial letter taken off is 'ear'.
'dr'+'ear'='DREAR'
(Other definitions for drear that I've seen before include "Dismal (literary)" , "Dull and tedious" , "Gloomy and cheerless" , "Poetic dull and uninteresting" , "Morose" .)