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