Bissextile

(sĕks'tīl), n. [Lat. 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 intercalation of a day. Ainsworth.] Leap year; every fourth year, in which a day is added to the month of February on account of the excess of the civil year (365 d. 5 h. 48 m. 49.7 s.) above 365 days. But one day added every four years is equivalent to six hours each year, which is 11 m. 10.3 s. too much, or more than 5 h. 48 m. 49.7 s., the excess of the real year. 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.

a. Pertaining to the leap year.