• Webster's Revised Unabridged Dictionary
    • n Bissextile Leap year; every fourth year, in which a day is added to the month of February on account of the excess of the tropical year (365 d. 5 h. 48 m. 46 s.) above 365 days. But one day added every four years is equivalent to six hours each year, which is 11 m. 14 s. more than the excess of the real year. Hence, it is necessary to suppress the bissextile day at the end of every century which is not divisible by 400, while it is retained at the end of those which are divisible by 400.
    • a Bissextile Pertaining to leap year.
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Century Dictionary and Cyclopedia
    • bissextile Containing the bissextus or intercalary day: applied to those years which have 366 days, the extra day being inserted in the month of February. See bissextus. This occurs every fourth year, taken as each year of which the number is divisible by 4 without remainder. Inasmuch, however, as a year of 365¼ days exceeds the true length of a solar astronomical year by 11 minutes and 14 seconds, amounting to an error of a day in 128 years, it was provided in the Gregorian calendar that the intercalary day should be omitted in all centenary years except those which are multiples of 400.
    • n bissextile A leap-year (which see).
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Chambers's Twentieth Century Dictionary
    • n Bissextile bis-sext′il leap-year
    • adj Bissextile containing the Bissext (L. bissextus), or extra day which the Julian calendar inserts in leap-year—the sixth before the kalends of March, 24th February
    • ***


Webster's Revised Unabridged Dictionary
L. bissextilis, annus, fr. bissextus, bis, + sextus, sixth, fr. sex, six) 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


In literature:

The bissextile is known to have been used by the Mayas, Tzendals, and Quiches, and it was probably common.
"Ancient America, in Notes on American Archaeology" by John D. Baldwin
This rule of the bissextile year, Rome, which is destined to endure to the end of time, established with the aid of the heavenly Deity.
"The Roman History of Ammianus Marcellinus" by Ammianus Marcellinus
Being the Third after Bissextile, or Leap-Year.
"A Catalogue of Books in English Later than 1700 (Vol 1 of 3)" by Various