Bitterness against reduced cashback (5)
I believe the answer is:
venom
'bitterness' is the definition.
(I've seen this in another clue)
'against reduced cashback' is the wordplay.
I cannot quite see how this works, but
'against' could be 'no' and 'no' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for venom that I've seen before include "Bitter malice" , "Virulent feeling" , "bitterness" , "Poison - spite" , "Spite: toxin" .)