Permit fighting rhetoric (7)
I believe the answer is:
warrant
'permit' is the definition.
(thesaurus)
'fighting rhetoric' is the wordplay.
'fighting' becomes 'war'.
'rhetoric' becomes 'rant' (rant is a kind of rhetoric).
'war'+'rant'='WARRANT'
(Other definitions for warrant that I've seen before include "Document giving authority" , "Guaranty - authorisation to make an arrest" , "Travel pass" , "Justify; authorisation" , "Permit for arrest, search of premises, etc" .)