Throw a backhander (4)
I believe the answer is:
bung
'throw' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for bung that I've seen before include "Plug for a hole in a small boat" , "sweetener" , "Bribe; throw" , "Large cork" , "Stopper for closing hole in barrel" .)