seriousyoudaoicibaDictYouDict[serious 词源字典]
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 etymology, serious origin, 英语词源]
serious (adj.)youdaoicibaDictYouDict
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.