To bribe with pound note is blunder (6)
I believe the answer is:
bungle
'is blunder' is the definition.
(I've seen this before)
'to bribe with pound note' is the wordplay.
'to bribe' becomes 'bung' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'pound' becomes 'L' (the pound sign is based on an L).
'note' becomes 'e' (musical note).
'bung'+'l'+'e'='BUNGLE'
(Other definitions for bungle that I've seen before include "Blunder" , "[BEAR]" , "Botch, make a hames of" , "Make a hash of the job" , "Clumsy mistake" .)