Definition
(Noun) One of the two periods in the year when the days and nights are equal in length all over the earth, owing to the sun’s crossing the equator. Hence, the precise moment at which the sun crosses the equator.
In Context
“Easter is defined as the first Sunday after the first full moon that appears on or after the spring equinox, March 20.”
Jack Ewing, Monkeys Are Made of Chocolate: Exotic and Unseen Costa Rica, 2005.