Gloomy bishop in northern town (5)
I believe the answer is:
'gloomy' is the definition.
'bishop in northern town' is the wordplay.
'bishop' becomes 'B' (chess abbreviation).
'in' means one lot of letters goes inside another.
'northern town' becomes 'sale' (I am not sure about this - if you are sure you should believe this answer much more).
'b' going into 'sale' is 'SABLE'.
Can you help me to learn more?
(Other definitions for sable that I've seen before include "Fur - heraldic black" , "Black; antelope" , "Dark brown fur of the marten" , "Antelope, fur" , "fur coat" .)