Polish by endless brushing, possibly (7)
I believe the answer is:
burnish
'polish' is the definition.
(I know that polish can be written as burnish)
'endless brushing possibly' is the wordplay.
'endless' means to remove the last letter.
'possibly' indicates anagramming the letters.
'brushing' with its last letter taken off is 'brushin'.
'brushin' is an anagram of 'BURNISH'.
'by' is the link.
(Other definitions for burnish that I've seen before include "Shine by rubbing" , "Make shiny by friction" , "Make bright by rubbing" , "Buff up" , "Polish by rubbing" .)