Smell of a small coin (5)
I believe the answer is:
scent
'smell of' is the definition.
(thesaurus)
'a small coin' is the wordplay.
'a small' becomes 's' (abbreviation - e.g. clothes size).
'coin' becomes 'cent' (cent is a kind of coin).
's'+'cent'='SCENT'
(Other definitions for scent that I've seen before include "Whiff" , "Pleasant smell" , "Distinctive odour" , "Distinctive aroma" , "Bouquet" .)