Differ, dissent (8)
I believe the answer is:
disagree
This clue is a double definition.
'differ' is the first definition.
(I know that differ can be written as disagree)
'dissent' is the second definition.
(I know that dissent can be written as disagree)
(Other definitions for disagree that I've seen before include "Quarrel" , "Have conflicting opinions" , "Contradict" , "Have differing opinions" , "Differ in opinion" .)