Epact

n. [ F. épacte, fr. Gr. 'epakto`s brought on or in, added, fr. 'epa`gein to bring on or in; 'epi` on, in + 'a`gein to bring or lead. See Epi-, and Act. ] (Chron.) The moon's age at the beginning of the calendar year, or the number of days by which the last new moon has preceded the beginning of the year. [ 1913 Webster ]

Annual epact, the excess of the solar year over the lunar year, -- being eleven days. --
Menstrual epact, or
Monthly epact, the excess of a calendar month over a lunar. [ 1913 Webster ]