Bitterness or ill-feeling (8)
I believe the answer is:
acrimony
This clue is a double definition.
'bitterness' is the first definition.
(I know that bitterness can be written as acrimony)
'ill-feeling' is the second definition.
(I've seen this before)
(Other definitions for acrimony that I've seen before include "poison" , "Asperity" , "Bad feeling" , "Acronym I construct with bitter words" , "I cry, moan (anag)" .)