Polish once more give a snub (6)
I believe the answer is:
rebuff
This clue is a double definition.
'polish once more' is the first definition.
('buff' is an answer for 'polish' so perhaps 'rebuff' is OK for 'polish once more')
'a snub' is the second definition.
(I know that snub can be written as rebuff)
'give' acts as a link.
(Other definitions for rebuff that I've seen before include "Snub or contemptuous refusal" , "Check" , "Beat back" , "Abrupt or ungracious rejection" , "Cold-shoulder" .)