Origin: 1545–55; < Late Latin epacta < Greek epaktḗ, noun use of feminine of epaktós added, equivalent to ep-ep- + ag(ein) to lead + -tos verbid suffix
1552, "number of days by which the solar year exceeds a lunar one of 12 moons;" also "number of days into the moon on which the solar year begins;" from Fr. epacte, from L. epacta, from Gk. epaktos, verbal adj. of epagein "to intercalate, add, bring forward," from epi "on" + agein "to bring, to lead"