Launch backhander (4)
I believe the answer is:
bung
'launch' is the definition.
(thesaurus)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for bung that I've seen before include "sweetener" , "Tip, bribe (sl.)" , "Bribe (slang)" , "Bribe - bottle stopper" , "illegal incentive" .)