Gloomy front door and back (5)
I believe the answer is:
drear
'gloomy' is the definition.
(I know that gloomy can be written as drear)
'front door and back' is the wordplay.
'front' suggests taking the first letters.
'and' means one lot of letters go next to another.
'back' becomes 'rear' (something's rear is its back).
The first letter of 'door' is 'd'.
'd'+'rear'='DREAR'
(Other definitions for drear that I've seen before include "Morose" , "grave" , "Poetic dull and uninteresting" , "gloomy in poem" , "Cheerless (literary)" .)