significant, important, momentous

形容詞 important:

1. of great significance or value
   同義詞：of import
2. important in effect or meaning
   同義詞：significant
3. of extreme importance; vital to the resolution of a crisis
   同義詞：crucial
4. having authority or ascendancy or influence
   同義詞：authoritative
5. having or suggesting a consciousness of high position

1. It was one of the most important discoveries ever made.
   這是所做出的最重大的發(fā)現(xiàn)之一。
2. He has made an important contribution to the company's success.
   他對公司的成功作出了重要的貢獻。
3. It is important that he not do it.
   他不該做那事是有必要的。
4. History chronicles important events of the past.
   歷史記載歷代重要的事件。
5. Radio and television are important means of communication.
   無線電和電視是重要的通信手段。
6. It's very important to teach the children about road safety.
   把交通安全常識教給孩子們是非常重要的。
7. It's not as if he was very important in the company hierarchy.
   他在公司的領導層中似乎無多大權力。
8. She was clearly an important person.
   她顯然是個有影響的人。

im.por.tant

adj.Abbr. imp.（形容詞）縮寫 imp.
Strongly affecting the course of events or the nature of things; significant:
重要的，有影響力的：強烈影響事件的進程或者事物的性質的；有特殊意義的：
例句：
an important message that must get through; close friends who are important to me.
必須傳達的重要的消息；對我來說非常重要的親密朋友

Having or suggesting a consciousness of high position or authority; authoritative:
顯要的，權威的：感覺到或顯示出高位或權威的；具有一種權威之神態(tài)的：
例句：
recited the decree with an important air.
以權威的姿態(tài)宣讀法令

Obsolete Importunate.
【廢語】 胡攪蠻纏的

來源：
Middle English
中古英語
from Old French
源自 古法語
from Medieval Latin import3ns important- [present participle of] import3re [to mean]
源自 中世紀拉丁語 import3ns important- [] import3re的現(xiàn)在分詞 [表示…的意思]
from Latin [to import] * see import
源自 拉丁語 [具重要性] *參見 import

【引伸】
impor.tantly
adv.（副詞）
Some critics have objected to the use of the phrasemore importantly in place of more important as a means of introducing an assertion, as inMore importantly, there is no party ready to step into the vacuum left by the Communists. But both forms are widely used by reputable writers,and there is no obvious reason for preferring one or the other.In an earlier surveythe introductory use ofmore importantly was acceptable to half of the members of the Usage Panel.
一些批評家已經(jīng)對短語more importantly 作為表述一個斷言的方法來代替短語 more important 提出反對意見， 如在句子更重要的是，沒有政黨準備進入共產黨留下來的真空中去。 但是這兩種形式都被有聲望的作家廣泛使用，并且沒有明顯的理由說哪個比哪個更好。在早期的調查中，more importantly 的引入使用對用法專題小組的半數(shù)成員來說是可以接受的