Definition of "epact" [e•pact]

• The period of time necessary to bring the solar calendar into harmony with the lunar calendar. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Osiris, and winning from her the five days of the epact, which were added to complete the 365 days of the year."
• "In Table III, under 9, and in the line C, we find the epact"
• "When P = 2 the new moon falls on the ninth, and the epact is consequently twenty-two; and, in general, when P becomes 1 + x, E becomes 23 - x, therefore P + E = 1 + x + 23 - x = 24, and"