Corrupt, gutless duke accepts being rebuffed (6)
I believe the answer is:
defile
'corrupt' is the definition.
(synonyms)
'gutless duke accepts being rebuffed' is the wordplay.
'gutless' means to remove the middle letters.
'accepts' means one lot of letters goes inside another.
'being' becomes 'life' (life is a kind of being).
'rebuffed' shows that the letters should be reversed in order.
'duke' with its middle taken out is 'de'.
'life' backwards is 'efil'.
'de' enclosing 'efil' is 'DEFILE'.
(Other definitions for defile that I've seen before include "Spoil; steep-sided gorge" , "Spoil; narrow gorge" , "Befoul" , "Soil" , "Corrupt - mountain pass" .)