bissextile day
noun
bis·sex·tile day
(ˈ)bī,
bə̇ +
: leap day
Word History
Etymology
Medieval Latin bissextilis, bisextilis of a bissextus, from Late Latin bissextus, bisextus, an intercalary day in the Julian calendar, from bi- bi entry 1 or bis- + sextus sixth; from its following February 24, the 6th day before the calends of March