Dull, gloomy (7)
I believe the answer is:
subfusc
I believe this is a double definition.
'dull' is the first definition.
(synonyms)
'gloomy' is the second definition.
(I've seen this before)
(Other definitions for subfusc that I've seen before include "dress for Zuleika Dobson?" , "Dull, gloomy; academic dress" , "Formal university wear" , "Surprisingly dull" , "Dull in colour" .)