'Monthly epact' definitions:

Definition of 'Monthly epact'

From: GCIDE

Epact \E"pact\ ([=e]"p[a^]kt), n. [F. ['e]pacte, 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]