authoritative

形容词 authoritative:

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

1. A formal and authoritative speech; an address.
   训示，训谕正式的并具权威性的讲话; 演讲
2. A fundamental set of rules having authoritative weight.
   十条戒律有权威性的一套基本规则
3. Don't speak in an authoritative tone.
   不要用一种命令的口吻说话。
4. This is an authoritative order.
   这是一个必须服从的命令。

au.thor.i.ta.tive

adj.（形容词）
Having or arising from authority; official:
官方的：有着或由政府发起的；官方的：
例句：
an authoritative decree; authoritative sources.
一项官方的法令；官方来源

Of acknowledged accuracy or excellence; highly reliable:
权威性的：拥有公认的精确性或优秀性的；极可信赖的：
例句：
an authoritative account of the revolution.
对变革的权威性报道

Wielding authority; commanding:
专断的：行使权力的；命令的：
例句：
the captain`s authoritative manner.
军官专断的行为方式

【引伸】
author.ita.tively
adv.（副词）
author.ita.tiveness
n.（名词）