The Collaborative International Dictionary
Quarantine \Quar"an*tine\, n. [F. quarantaine, OF. quaranteine, fr. F. quarante forty, L. quadraginta, akin to quattuor four, and E. four: cf. It. quarantina, quarentine. See Four, and cf. Quadragesima.]
A space of forty days; -- used of Lent.
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Specifically, the term, originally of forty days, during which a ship arriving in port, and suspected of being infected a malignant contagious disease, is obliged to forbear all intercourse with the shore; hence, such restraint or inhibition of intercourse; also, the place where infected or prohibited vessels are stationed.
Note: Quarantine is now applied also to any forced stoppage of travel or communication on account of malignant contagious disease, on land as well as by sea.
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(Eng. Law) The period of forty days during which the widow had the privilege of remaining in the mansion house of which her husband died seized.
Quarantine flag, a yellow flag hoisted at the fore of a vessel or hung from a building, to give warning of an infectious disease; -- called also the yellow jack, and yellow flag.
Wiktionary
n. (context nautical English) a yellow flag hoisted by all ships on entering a harbor, to show that it has contagious or infectious disease aboard, or by a ship that has been quarantined
Usage examples of "quarantine flag".
The Dannebrog broke out at the Sophie's gaff-end, followed by the yellow quarantine flag at the fore.
Scotty identified it as the quarantine boat, and pointed out that the trawler was flying the yellow quarantine flag, a matter of routine on entering a strange port.