严肃的的英文：
grave
serious
severe
smileless
sober
solemn

参考例句：

deadly seriousness
极为严肃的

Solemnity or dignity of manner.
严肃或庄严的举止

An earnest admonition or reproof;a reprimand.
严肃的劝诫或责怪;斥责

You should be serious in class. Don't behave in a noisy, gay, and boisterous manner.
你上课要严肃，不准嬉皮笑脸。

The consular official wore a rather solemn expression.
领事馆官员脸上的表情相当严肃。

Pierce's open, freckled face was grave
皮尔斯那张有雀斑的大脸庞显得严肃庄重。

The airwaves are noisy with nonsense at a time when we need serious, substantive information.
当我们需要严肃而真实的信息的时候，电视广播却是充斥着废话的噪声。

This light-hearted award helps underscore just how dominant the World No.1 player was in2006.
这个不那么严肃的奖项更能看出2006年世界头号选手的实力。

A person regarded as obnoxiously puritanical.
清教徒的禁欲主义，严肃拘谨的人被认为令人反感的清教徒式的人

My unsoiled name, the austereness of my life, my word vouched against yours, will outweigh your accusation.
我的纯洁无瑕的名声，我那严肃的生活，我那些反驳你的话，都足够压倒你的控诉的。

grave是什么意思：
n. 坟墓；死亡
adj. 重要的；严重的；严肃的
v. 雕刻；铭记

Grave Busters consume graves they’re planted on.
噬碑藤会将它被种植在其上的墓碑吞噬。

The abductee issue is of grave concern.
绑架问题值得严重关切。

To have one foot in the grave
风烛残年

serious是什么意思：
adj. 严肃的，认真的；严重的；危急的；重要的；庄重的

It is a serious article.
这是一篇发人深省的文章。

do not deny that is a serious blow.
我不否认那是严重的一击。

It is a job requiring serious application.
这是一项需要非常勤奋的工作。

severe是什么意思：
adj. 严重的；严厉的；严格的；严峻的；严肃的，纯洁的

Rape several women or have sexual relations with several girls
强奸妇女、奸淫幼女多人的

This assumption is false in several ways.
这种推断是错误的，错在了多个方面。

It comes with several inbuilt features.
他有很多固定的特征。