D defs.my
Entry 1 sense Webster, 1913

Epact

/(ē"păkt)/ · E·pact · IPA
01 n. 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.
  1. 1.
    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.(Chron.)
Phrases & compounds
Annual epact — the excess of the solar year over the lunar year, -- being eleven days.
Menstrual epact — the excess of a calendar month over a lunar.