Quarantine entered English in the 16th century, coming from Italian quarantina, meaning ‘forty days’, from quaranta ‘forty’. It denoted a period of forty days during which a newly widowed woman was entitled to remain in her late husband's house. The current sense is first recorded in 1663, in Samuel Pepys's Diary. From then on the emphasis of the word was on the state of isolation rather than the number of days (which depended on the incubation period of the disease in question).