Referring to a period of isolation enforced on a person (or, originally, a ship) suspected of carrying an infectious disease, the word quarantine is derived from the Italian word for ‘forty’, quarantina, as this period of isolation was originally always forty days long.
This medical use of the word dates from the mid-seventeenth century in English, but the term had in fact been in use for several centuries before this meaning arose. Which brings us to a perennial HH favourite fact, which popped up again on the Twitter feed yesterday: a quarantine was originally the period of time a widow was legally permitted to remain in her deceased husband’s home.
No prizes for figuring out that this legal period was also originally forty days long—and indeed, a host of other older meanings of quarantine refer to other similar lengths of time.
In religious contexts, quarantine was once used as a name for the desert in which Jesus fasted for forty days and forty nights (1400s), and the name of a forty-day period of penance observed in the Christian Church (1600s).
All of these older uses of the word derive directly from the Latin word for ‘forty’, quadraginta, from which English has also taken quadragene, a forty-day recession of punishment after confession in the Catholic Church, and Quadragesima, the forty days comprising Lent in the Christian calendar.