Quarantine originally referred to a specific length of time: forty days. The English word comes through Italian, from quaranta, meaning forty. In ports such as Venice, ships arriving during times of plague could be kept apart before passengers or goods were allowed ashore.
That waiting period became known as quarantino, literally a forty day separation. The goal was to reduce the chance of disease spreading into the city.
Today, the meaning is broader. Quarantine usually means keeping people, animals, or goods apart for a period of time because of possible exposure to disease. The period is no longer tied to the number forty.
- A traveler may quarantine for a few days after exposure.
- An animal may be placed in quarantine before entering a country.
- A shipment of plants can be held in quarantine to prevent pests or disease.
So the word began with a precise number, but modern usage keeps the idea of separation for safety, not the original forty day limit.