Wildly boo a preacher, vicar initially blameless (5,8)
I believe the answer is:
above reproach
'blameless' is the definition.
'wildly boo a preacher vicar initially' is the wordplay.
'wildly' is an anagram indicator.
'initially' says to take the initial letters.
The initial letter of 'vicar' is 'v'.
'boo'+'a'+'preacher'+'v'='booapreacherv'
'booapreacherv' with letters rearranged gives 'ABOVE REPROACH'.
(Other definitions for above reproach that I've seen before include "Blameless -- totally honest" , "of unimpeachable quality" , "Beyond criticism" , "Not criticisable" , "Too good for criticism" .)