Differ (8)
'differ' is the definition.
(synonyms)
This is all the clue.
(Other definitions for disagree that I've seen before include "Differ in opinion" , "Differ, take issue" , "Be at odds" , "Take a different view" , "Take issue with, hold different opinion" .)
'differ' is the definition.
(varying is a kind of differing)
This is all the clue.
(Other definitions for vary that I've seen before include "Change, amend" , "Change, modify" , "Differ; change" , "Change according to circumstances" , "Change, diverge, deviate" .)