形容詞 authoritative:

1. having authority or ascendancy or influence
   同義詞：important
2. of recognized authority or excellence
   同義詞：classical, definitive
3. sanctioned by established authority
   同義詞：authorized, authorised

1. A formal and authoritative speech; an address.
   訓(xùn)示，訓(xùn)諭正式的并具權(quán)威性的講話; 演講
2. A fundamental set of rules having authoritative weight.
   十條戒律有權(quán)威性的一套基本規(guī)則
3. Don't speak in an authoritative tone.
   不要用一種命令的口吻說話。
4. This is an authoritative order.
   這是一個必須服從的命令。

au.thor.i.ta.tive

adj.（形容詞）
Having or arising from authority; official:
官方的：有著或由政府發(fā)起的；官方的：
例句：
an authoritative decree; authoritative sources.
一項官方的法令；官方來源

Of acknowledged accuracy or excellence; highly reliable:
權(quán)威性的：擁有公認(rèn)的精確性或優(yōu)秀性的；極可信賴的：
例句：
an authoritative account of the revolution.
對變革的權(quán)威性報道

Wielding authority; commanding:
專斷的：行使權(quán)力的；命令的：
例句：
the captain`s authoritative manner.
軍官專斷的行為方式

【引伸】
author.ita.tively
adv.（副詞）
author.ita.tiveness
n.（名詞）