Smell nothing grim (5)
I believe the answer is:
odour
'smell' is the definition.
(I know that smell can be written as odour)
'nothing grim' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'grim' becomes 'dour' (synonyms).
'o'+'dour'='ODOUR'
(Other definitions for odour that I've seen before include "Whiff" , "A smell, good or bad" , "Any property detected by the olfactory system" , "Distinctive smell" , "Smell; repute" .)