1. The number of days by which the solar year exceeds the lunar year; used in calculating the date of Easter and other movable feasts.
Usage: technical; ecclesiastical; plural of epact

Examples

• The epacts are essential for determining the lunar calendar's alignment with the solar calendar.
• Medieval monks used epacts to calculate the correct date for Easter each year.
• The table of epacts helped ecclesiastical authorities synchronize religious observances.
• Astronomers and theologians studied epacts to understand calendar systems.
• The epacts vary from year to year as the lunar and solar cycles drift apart.