Bitter resentment (7)
I believe the answer is:
rancour
'bitter resentment' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rancour that I've seen before include "Deep-seated enmity" , "Bitter resentment" , "Bitterness or resentfulness" , "Hard feelings" , "Malicious hostility" .)