Metonic cycle

noun

Me·​ton·​ic cycle

meˈtänik-

: a period of 19 years after the lapse of which the phases of the moon return to a particular date in the calendar year:

a

: one of the 19-year periods reckoning from June 27, 432 b.c. that were used in determining lengths of years and the placing of the intercalary month in the ancient Greek calendar

b

: one of the 19-year periods reckoning from 1 b.c. that are used in determining the date of Easter in the Gregorian calendar

Word History

Etymology

Meton, 5th century b.c. Greek astronomer + English -ic

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