A vile tale about moderate (9)
I believe the answer is:
alleviate
'moderate' is the definition.
(thesaurus)
'a vile tale about' is the wordplay.
'about' indicates an anagram.
'vile'+'tale'='viletale'
'viletale' is an anagram of 'lleviate'.
'a'+'lleviate'='ALLEVIATE'
(Other definitions for alleviate that I've seen before include "Lessen strength of" , "Make (pain) less intense" , "Ease" , "Lighten" , "Make less severe as with pain" .)