Relentlessly gloomy (4)
I believe the answer is:
dour
'relentlessly gloomy' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dour that I've seen before include "Gloomy or sullen" , "Grim, morose" , "Severe, stern, gloomy" , "Uncompromising" , "Constituent parts" .)