Find lie about unbeliever (7)
I believe the answer is:
infidel
'unbeliever' is the definition.
(I've seen this before)
'find lie about' is the wordplay.
'about' is an anagram indicator.
'find'+'lie'='findlie'
'findlie' with letters rearranged gives 'INFIDEL'.
(Other definitions for infidel that I've seen before include "Non-believer, heretic" , "Sceptical" , "Unbeliever" , "One not believing" , "Person not operating in good faith" .)