Epact

Part of speech: noun

Definitions

1. The concept captures the difference in days between the solar calendar and the lunar calendar, indicating how many extra days the lunar system has in a year to align with solar cycles
2. It describes the gap in days between the two calendars, reflecting how much longer the lunar year lasts compared to the solar year for determining specific dates
3. The term refers to the numerical difference in days required to synchronize the lunar calendar with the solar calendar, highlighting their annual discrepancies

Etymology: The epact is the number of days by which the lunar year falls short of the solar year, a figure calendar-makers needed in order to work out when the Paschal full moon would fall. The word comes from French "épacte", borrowed from Latin "epactae", which in turn came from Ancient Greek "ἐπακταί" (epaktaí), meaning "intercalary days". Those were the extra days added to a calendar to keep it in step with the seasons. The Greek word is the feminine plural of "ἐπακτός" (epaktós), "brought on or in, added". Its root idea is simply something introduced from outside a fixed sequence, which is exactly what the epact measured: the surplus days tucked into the lunar count so that the moon and the sun stayed reconciled.