authoritative
au-thor-i-ta-tive
adjective
Exercising power or control; confidently assertive and commanding.
"She spoke with an authoritative voice."
adjective
Based on sound knowledge; reliable and commanding respect.
"The report was an authoritative source of information."
Thesaurus
Synonyms: sanctioned, sceptered, empowered, authorized, authorised, canonized, canonised, sceptred, approved, glorified, standard, definitive
Antonyms: unauthorised, unauthorized