bis·sex·tile 
(bī-sĕkstĭl, -stīl′, bĭ-)
(bī-sĕkstĭl, -stīl′, bĭ-)adj.
1. Of or relating to a leap year.
2. Of or relating to the extra day falling in a leap year.
n.
A leap year.
[Late Latin bissextīlis, containing an intercalary day, from bisextus (diēs), bis sextus (diēs) and Latin bisextum, intercalary day : bis, twice; see BIS + sextus, sixth (because the sixth day before the Calends of March on February 24 occurred twice every leap year); see SEXT1.]