What does “fort” in “fortnight” mean?

Fortnight is a contraction of fourteen nights. The latter phrase, in the sense of a period of two weeks, was used in England as early as 1000 A.D., when it was used in a translation of the laws of Ine, who was King of the West Saxons in the seventh century. Fortnight has been gradually faU[.410.] Fing into disusej being supplanted by two weejfcs, particularly in the “United States. Sennight, another similar old English word now almost out of use, is a contraction of seven nights. Both fortnight and sennight occur several times in Shakespeare. Under date of October 9, 1711, William Byrd of Westover noted in his secret diary: “I told him I would meet hirtf at Colonel Harrison’s this day sennight and so took my leave,” These terms, fortnight and sennight, are probably survivals of an old Teutonic method of reckoning time by nights instead of by days. In 98 A.D. Tacitus wrote as follows of the ancient Germans: “Their account of time.differs from that of the Romans: instead of days, they reckon the number of nights. Their public ordinances are so dated; and their proclamations run in the same style. The night, according to them, leads the day.” In this connection it is interesting to recall that the American Indians reckoned time by moons, not by suns. Some Indians counted full days as so many nights or “sleeps.”