[1] : The Collaborative International Dictionary of English v.0.48

quarantine \quar"antine\, 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.
   1. a space of forty days; -- used of lent.
      1913 webster

   2. 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.
      1913 webster

   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.
         1913 webster

   3. 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.
      1913 webster

   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.
      1913 webster
see also:
four quadragesima quarantine flag yellow jack yellow flag 

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