[ad. Fr. epacte, L. epacta, Gr. ἐπακτή, f. ἐπακτός, vbl. adj. of ἐπάγειν to intercalate, f. ἐπί on + ἄγειν to bring.]

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  1.  a. (Also pl. epacts.) The number of days that constitutes the excess of the solar over the lunar year of 12 months. b. The number of days in the age of the moon on the first day of the year (now Jan. 1st, but formerly March 1st or 22nd).

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  a.  1588.  A. King, trans. Canisius’ Catech., N vj b. Ye Epact, quhilk is Ye nombre of ye dayes quhairby ye ȝere of ye sone do exceid ye ȝere of ye moone.

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1603.  Sir C. Heydon, Jud. Astrol., xviii. 383. The Epact or 11. daies ouerplus.

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1725.  Bradley, Fam. Dict., s.v. Year, These eleven Days are call’d Epacts.

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1750.  Phil. Trans., XLVI. 421.

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1787.  Bonnycastle, Astron., xiv. 237.

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  b.  1552.  Bk. Com. Prayer, Almanack, heading, of col. 3 The Epacte.

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1561.  Eden, Arte Nauig., II. vi. 31. This nomber of Epact or concurrent is founde.

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1594.  Blundevil, Exerc., VII. i. (ed. 7), 654. The Epact [beginneth] the first of March.

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1594.  J. Davis, Seamans Secr. (1607), B 3 b. There are 2. numbers especially required, named the Prime and the Epact.

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1696.  Whiston, Th. Earth, II. (1722), 214. The Eccentricity of the Sun is … exactly coincident with the Epact of the Moon.

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1704.  Hearne, Duct. Hist. (1714), I. 5. The EPACT is the number of Days of the Moon’s Age on the last Day of December.

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1704.  J. Harris, Lex. Techn., s.v., Divide by 3; for each one left add Ten; 30 reject: the Prime makes Epact then.

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1816.  Playfair, Nat. Phil., II. 137. The Epacts … the ages of the moon … at the beginning of every year.

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1867.  Denison, Astron. without Math., 95. The moon’s age at that time is called the epact of the year.

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  2.  Any intercalated day or days. rare.

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1603.  Holland, Plutarch’s Mor., Gloss., Epact, The day put to, or set in, to make the leape yeere.

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1880.  F. Lenormant, in Contemp. Rev., April, 585. The five days which the Egyptians added by way of epact to the twelve months of thirty days.

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  3.  attrib.

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1876.  Prayer-bk. Interleaved, 55. By means of the Epact Almanack, Easter-day for any year may be readily found.

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