Unopened perfume's grim (4)
I believe the answer is:
dour
'grim' is the definition.
('dour' can be a synonym of 'grim')
'unopened perfume's' is the wordplay.
'unopened' means to remove the first letter.
'perfume' becomes 'odour' (I've seen this before).
'odour' with its initial letter taken away is 'DOUR'.
(Other definitions for dour that I've seen before include "Gloomy-looking, stern" , "Gloomy in manner or appearance" , "Severe and gloomy looking" , "Morose, sour" , "Constituent parts" .)