epact

[ee-pakt]

noun

1. the difference in days between a solar year and a lunar year.

2. the number of days since the new moon at the beginning of the calendar year, January 1.

epact

/ ˈiːpækt /

noun

1. the difference in time, about 11 days, between the solar year and the lunar year

2. the number of days between the beginning of the calendar year and the new moon immediately preceding this

3. the difference in time between the calendar month and the synodic month

Word History and Origins

Origin of epact¹

1545–55; < Late Latin epacta < Greek epaktḗ, noun use of feminine of epaktós added, equivalent to ep- ep- + ag ( ein ) to lead + -tos verbid suffix

Word History and Origins

Origin of epact¹

C16: via Late Latin from Greek epaktē, from epagein to bring in, intercalate, from agein to lead

Example Sentences

Epact — a play on a medieval word for the age of the moon on the first of the year — is the result of a pact of sorts between four European institutions: the Museum of the History of Science in Oxford; the Museo Galileo in Florence; the British Museum in London; and the Museum Boerhaave in Leiden, Netherlands.

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And they’re on full display at Epact.

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Epact may make you appreciate the artistry and intricacy of now-obsolete scientific tools or leave you starry-eyed over each instruments’ function and a role.

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Either way, a visit to Epact is a glimpse into a bygone world — one in which scientists dared to dream and discover.

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In its final report, the EPAct Task Force explained that:

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