Approved, definitive (13)
I believe the answer is:
authoritative
This clue is a double definition.
'approved' is the first definition.
(thesaurus)
'definitive' is the second definition.
(synonyms)
(Other definitions for authoritative that I've seen before include "Factual" , "Reliable, true" , "Commanding, self-confident" , "Vested with power or influence" , "Commanding and self-assured" .)