BISSEX'TILE, noun [Latin bissextilis, leap year, from bissextus, [bis and sextus] the sixth of the calends of March, or twenty-fourth day of February, which was reckoned twice every fourth year, by the interrelation of a day.]
Leap year; every fourth year, in which a day is added to the month of February, on account of the excess of 6 hours, which the
civil year contains, above 365 days. This excess is 11 minutes 3 seconds too much; that is, it exceeds the real year, or annual revolution of the earth. Hence at the end of every century, divisible by 4, it is necessary to retain the bissextile day, and to suppress it at the end of those centuries which are not divisible by 4.
BISSEX'TILE, adjective Pertaining to the leap year.