quarantine

ˈkwȯr-ən-ˌtēn

Merriam-Webster’s Etymology section lists English quarantine as partly French quarantaine and partly Italian quarantena, both from Latin quadraginta, “forty.”

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Sailboat on calm harbor water at sunrise beside a stone lighthouse and breakwater. — Decorative illustration

2 source paths

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French source

Latinquadragintaforty
Frenchquarantainefrom quarante (“forty”) via Old French quarantaine
Englishquarantinepartly from French quarantaine

Italian source

Latinquadragintaforty
Italianquarantena“quarantine of a ship,” from quaranta, “forty”
Englishquarantinepartly from Italian quarantena

Forty days at sea

Merriam-Webster’s Etymology section lists two partial sources for English quarantine. The French line runs from Latin quadraginta through quarante (“forty”) and Old French to French quarantaine; the Italian line runs from Latin quadraginta through quaranta (“forty”) to Italian quarantena (“quarantine of a ship”). Merriam-Webster records the English noun in 1617; the Online Etymology Dictionary dates the ship-isolation sense to the 1660s, and the American Heritage Dictionary runs the word through Venetian quarantena.

This page summarizes the cited dictionary entries. Follow each source for its full wording, notes and references.

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Word-specific details from the linked dictionaries, with the dictionary named beside each claim.

Forty days, named

The number is the point. The Online Etymology Dictionary explains the name from the Venetian policy — first enforced in 1377 — of holding ships from plague-stricken places off the port for forty days; Italian quaranta giorni is literally “space of forty days.” Latin quadraginta, “forty,” sits beside quattuor, “four,” under the reconstructed root *kwetwer-.

That root family is visible in English too: the same dictionary's root entry lists forty, four, fortnight, quire and square among the words it might form — the forty inside quarantine is the documented one.

Before it meant isolation

Forty was doing work in English before the ships. The Online Etymology Dictionary records quarantine meaning a widow's forty-day right to remain in her dead husband's house in the 1520s, and quarentyne in the 15th century for the desert in which Christ fasted forty days — all built on the same Latin quadraginta.

The modern breadth came after: the extended sense of “any period of forced isolation” is from the 1670s, and the American Heritage Dictionary's entry now includes the computing sense — isolating data to keep malware from spreading.

Two dictionaries, two dates

Merriam-Webster dates the English noun to 1617 and the verb to 1801; the Online Etymology Dictionary dates the ship-isolation noun to the 1660s and the verb to 1804. Both pairs of dates are kept here, scoped to their dictionary, rather than smoothed into one.

And the 1377 date belongs to the Venetian policy — the institution that supplied the name — not to the English word itself. Keeping those apart is the difference between a word's record and the practice's record.

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