以下这些形容词均有"严肃的" 的意思
earnest：指严肃，认真，含诚恳和热情意味。
serious：指具有关键、严肃或严重意义的事情。
grave：侧重严肃和尊严，需要认真思考，含令人担忧意味。
severe：指面孔的严肃，法律的严厉，伤病的严重。着重严厉性，无丝毫温情。
solemn：指人表情或场景气氛严肃，侧重威严名印象深刻。
sober：侧重因控制或抑制自己的感情而表现出的庄重。

词组

as sober as a judge
completely sober 非常清醒的
sober up; sober somebody up
(使) 醒酒

英语六级真题

I turn to eccentric measures to try to keep my mind sober and ensure that I have time to do nothing at all (which is the only time when I can see what I should be doing the rest of the time).

出自-2012年12月阅读原文

Eccentric measures are needed to keep one's mind sober

出自-2012年12月阅读原文

柯林斯高阶英汉双解学习词典释义

ADJ-GRADED

清醒的;没喝醉的

When you are sober, you are not drunk.
例句
When Dad was sober he was a good father. 不喝醉的时候，爸爸是一个好父亲。
ADJ-GRADED

严肃的;审慎的;头脑清醒的

A sober person is serious and thoughtful.
例句
We are now far more sober and realistic... 我们现在清醒、现实多了。 It was a room filled with sad, sober faces... 房间里坐满了人，大家都一脸的忧伤和严肃。
ADJ-GRADED

(颜色、衣服)素淡的，素净的，古板的

Sober colours and clothes are plain and rather dull.
例句
He dresses in sober grey suits. 他总是穿素净的灰西服。 ...sober-suited middle-aged men. 衣着素淡的中年男子

英汉词典释义

adj.
没喝醉的; 头脑清醒的; 未醉的
The man was still sober when he went home. 那人回到家时头脑依然清醒。 Anyone who is not drunk is sober. 任何没有喝醉的人都头脑清醒。
(人及其行为) 持重的; 冷静的
He is honest, sober and hard-working. 他诚实、稳重、勤奋。
vt. & vi.
(使)变得持重; 亦得冷静
The bad news sobered us a while. 坏消息使我们冷静了一会儿。 He suddenly sobered. 他突然严肃起来。

英英词典释义

Verb
1. cause to become sober;
"A sobering thought"
2. become more realistic;
"After thinking about the potential consequences of his plan, he sobered up"
3. become sober after excessive alcohol consumption;
"Keep him in bed until he sobers up"
Adjective
1. not affected by a chemical substance (especially alcohol)
2. dignified and somber in manner or character and committed to keeping promises;
"a grave God-fearing man""a quiet sedate nature""as sober as a judge""a solemn promise""the judge was solemn as he pronounced sentence"
3. lacking brightness or color; dull;
"drab faded curtains""sober Puritan gray""children in somber brown clothes"
4. completely lacking in playfulness