Smell of a coin, say (5)
I believe the answer is:
scent
'smell of' is the definition.
(thesaurus)
'a coin say' is the wordplay.
'a coin' becomes 'cent' (cent is a kind of coin).
'say' shows a homophone (sound like).
'cent' is a homophone of 'SCENT'.
(Other definitions for scent that I've seen before include "Clue" , "Fragrance" , "Trail" , "Number of clues" , "Pleasant smell" .)