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

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