Avenge quieter eccentric (7)
I believe the answer is:
requite
'avenge' is the definition.
(thesaurus)
'quieter eccentric' is the wordplay.
'eccentric' indicates an anagram.
'quieter' with letters rearranged gives 'REQUITE'.
(Other definitions for requite that I've seen before include "Make return" , "Quieter (anag.)" , "Appropriately, give back" .)