quarantineyoudaoicibaDictgodict[quarantine 词源字典]
quarantine: [17] Quarantine denotes etymologically a period of ‘forty’ days. It goes back ultimately to Latin quadrāgintā ‘forty’, whose Italian descendant quaranta formed the basis of the noun quarantina ‘period of forty days’. English used it originally for a ‘period of forty days’ isolation’, but gradually the stipulation of the number of days faded out.
=> quarter[quarantine etymology, quarantine origin, 英语词源]
quarantine (n.)youdaoicibaDictgodict
1520s, "period of 40 days in which a widow has the right to remain in her dead husband's house." Earlier quarentyne (15c.), "desert in which Christ fasted for 40 days," from Latin quadraginta "forty," related to quattuor "four" (see four).

Sense of "period a ship suspected of carrying disease is kept in isolation" is 1660s, from Italian quarantina giorni, literally "space of forty days," from quaranta "forty," from Latin quadraginta. So called from the Venetian custom of keeping ships from plague-stricken countries waiting off its port for 40 days (first enforced 1377) to assure that no latent cases were aboard. The extended sense of "any period of forced isolation" is from 1670s.
quarantine (v.)youdaoicibaDictgodict
1804, from quarantine (n.). Related: Quarantined; quarantining.