Bitterness, resentment (7)
I believe the answer is:
rancour
I believe this is a double definition.
'bitterness' is the first definition.
(I know that bitterness can be written as rancour)
'resentment' is the second definition.
(I know that resentment can be written as rancour)
(Other definitions for rancour that I've seen before include "Deep-seated enmity" , "Spiteful ill-feeling" , "Malice" , "Hard feelings" , "Bitterness and ill will" .)