authoritative

Adjective

Synonyms: important classical classic definitive authorized authorised

WordNet 3.0

Adjective (3)

having authority or ascendancy or influence“an important official”“the captain's authoritative manner”Synonyms: important
of recognized authority or excellence“the definitive work on Greece”“classical methods of navigation”Synonyms: classical classic definitive
sanctioned by established authority“an authoritative communique”“the authorized biography”Synonyms: authorized authorised

Webster's Dictionary (GCIDE)

Authoritative \Au*thor"i*ta*tive\, a.

1.Having, or proceeding from, due authority; entitled to obedience, credit, or acceptance; determinate; commanding. [1913 Webster]

The sacred functions of authoritative teaching.— Barrow.[1913 Webster]

2.Having an air of authority; positive; dictatorial; peremptory; as, an authoritative tone. [1913 Webster]

The mock authoritative manner of the one, and the insipid mirth of the other. --Swift. [1913 Webster] -- Au*thor"i*ta*tive*ly, adv. -- Au*thor"i*ta*tive*ness, n. [1913 Webster]