Small, inferior track (5)
I believe the answer is:
spoor
'track' is the definition.
(I know that spoor is a type of trail)
'small inferior' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'inferior' becomes 'poor' (similar in meaning).
's'+'poor'='SPOOR'
(Other definitions for spoor that I've seen before include "Beast's trail" , "Animal track or scent" , "Animal's track or scent" , "24 [TRAIL]" , "Animal's track/scent" .)