Bissextus

Lat. [from bis, twice, and sextus, sixth.] In old English law. The added, repeated or increasing day (dies excrescens) of a leap year; in the Roman calendar, the sixth day before the calends of March, twice computed. It was made up of the odd hours and minutes over 365 days, which had been disregarded in the three preceding years, in addition to those of the fourth year, (ex minutiis quatuor annorum.) Bract. fol.

359 b.