epact (n.) Look up epact at Dictionary.com
1550s, "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 French épacte (12c.), from Late Latin epacta "an intercalary day," from Greek epaktos, literally "brought in, inported," verbal adjective of epagein "to intercalate, add, bring forward," from epi "on" (see epi-) + agein "to bring, to lead" (see act (v.)).