Small coin leaves trail (5)
I believe the answer is:
scent
'trail' is the definition.
(an animal's trail is its scent)
'small coin' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'coin' becomes 'cent' (cent is a kind of coin).
's'+'cent'='SCENT'
'leaves' acts as a link.
(Other definitions for scent that I've seen before include "Pleasant odour" , "Trail" , "Track; aroma" , "Distinctive smell" , "Bouquet" .)