Change is ever-changing (6)
I believe the answer is:
revise
'change' is the definition.
(thesaurus)
'is ever-changing' is the wordplay.
'changing' indicates an anagram.
'is'+'ever'='isever'
'isever' with letters rearranged gives 'REVISE'.
(Other definitions for revise that I've seen before include "Mug up" , "Go back over lesson" , "Make changes to" , "Edit" , "Improve, amend" .)