serious

1、serious 的老根是 PIE *swer-"重"：serious 本义"有分量的"——事重、人郑重。德语 schwer（重的）是远亲，汉语说"重要"也借同一个重量比喻，好记。
2、拼写别塌：se-ri-ous 三个元音连着走，读 /ˈsɪə.ri.ə.s/；别写成 serius。Are you serious?（你认真的？/没开玩笑？）是口语高频。
3、"严肃"辨析一圈：solemn 带威严庄重（仪式感），severe 严厉到没温情（纪律、伤痛），sober 是压住情绪的冷静清醒，serious 泛指"认真、严重"这层最常用的意思。

serious 严重的，严肃的，认真的

来自拉丁语 serius,严重的，严肃的，认真的，来自 PIE*swer,重的。

serious

serious: [15] Serious comes ultimately from Latin sērius ‘serious, grave’. From this was derived late Latin sēriōsus, which passed into English via Old French serieux. It is not clear where sērius came from, although some have linked it with German schwer ‘heavy’ (‘seriousness’ and ‘weightiness’ being semantically close).

serious (adj.)

mid-15c., "expressing earnest purpose or thought" (of persons), from Middle French sérieux "grave, earnest" (14c.), from Late Latin seriosus, from Latin serius "weighty, important, grave," probably from a PIE root *swer- (4) "heavy" (cognates: Lithuanian sveriu "to weigh, lift," svarus "heavy;" Old English swære "heavy," German schwer "heavy," Gothic swers "honored, esteemed," literally "weighty"). As opposite of jesting, from 1712; as opposite of light (of music, theater, etc.), from 1762. Meaning "attended with danger" is from 1800.

1. I know it's nothing serious and I feel quite unemotional about it.

我知道那根本没什么大不了的，所以有些无动于衷。

2. Smoking places you at serious risk of cardiovascular and respiratory disease.

吸烟会大大增加罹患心血管和呼吸道疾病的风险。

3. She was fitted with a pacemaker after suffering serious heart trouble.

她患上严重的心脏病后安装了心脏起搏器。

4. The allegations are serious enough to warrant an investigation.

这些指控很严重，有必要进行一番调查。

5. He sustained serious neck injuries after he broke someone's fall.

有人坠落压在他身上，致使他颈部受重伤。

【solemn, sober, earnest, grave, severe, serious】
这组词都有“严肃的”的意思，其区别是：
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。
earnest: 指严肃，认真，含诚恳和热情意味。
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。
serious: 指具有关键、严肃或严重意义的事情。