I learnt last night that the word quarantine, as in “a restriction on the movement of people and goods which is intended to prevent the spread of disease or pests”, comes from Venetian word meaning forty, quarantina, which comes from quarantina giorni (forty days). Quarantina comes from quaranta (forty), from the Latin quadrāgintā (forty).

During the 14th and 15th centuries there were several outbreaks of the bubonic plague in Europe. At that time there was a practise of requiring ships to wait for a period of time before entering Venice or Ragusa (modern Dubrovnik in Croatia), which was ruled by Venice at the time. Initally the crew and passengers had to wait 30 days on their ships or on nearby islands. This period was extended to 40 days by the Venetian Senate in 1448.

Sources: Wiktionary & Wikipedia