A small and a large shoe (6)
I believe the answer is:
sandal
'shoe' is the definition.
(sandal is a kind of shoe)
'a small and a large' is the wordplay.
'a small' becomes 's' (abbreviation - e.g. clothes size).
'large' becomes 'l'.
's'+'and'+'a'+'l'='SANDAL'
(Other definitions for sandal that I've seen before include "One can go on foot" , "what may be afoot" , "Wood" , "An open shoe for summer" , "Item of footwear" .)