Emily Dickinson Lexicon

QUAR'AN-TINE, n. [It. quarantina, forty; Sp. quarentena; Fr. quarantaine; from the root of L. quartus, fourth, Fr. carreau, a square, carrer, to square, Arm. carrea, to square, W. cwar, square, Eng. quart. See Quart and Square.]

1. Properly, the space of forty days; appropriately, the term of forty days during which a ship arriving in port and suspected of being infected with a malignant, contagious disease, is obliged to forbear all intercourse with the city or place. Hence,
2. Restraint of intercourse to which a ship is subjected on the presumption that she may be infected, either for forty days or for any other limited term. It is customary for the proper officers to determine the period of restraint at their discretion, according to circumstances. Hence we hear of a quarantine of five days, of ten, of thirty, &c. as well as of forty. We say, a ship performs quarantine, or rides at quarantine. We also apply the word to persons. The passengers and crew perform quarantine.
3. In law, the period of forty days, during which the widow of a man dying seized of land, has the privilege of remaining in the mansion house.