noun the date at which a planet or comet has a longitude or position.
2. epoch ·noun a division of time characterized by the prevalence of similar conditions of the earth; commonly a minor division or part of a period.
3. epoch ·noun a period of time, longer or shorter, remarkable for events of great subsequent influence; a memorable period; as, the epoch of maritime discovery, or of the reformation.
4. epoch ·noun an arbitrary fixed date, for which the elements used in computing the place of a planet, or other heavenly body, at any other date, are given; as, the epoch of mars; lunar elements for the epoch march 1st, 1860.
5. epoch ·noun a fixed point of time, established in history by the occurrence of some grand or remarkable event; a point of time marked by an event of great subsequent influence; as, the epoch of the creation; the birth of christ was the epoch which gave rise to the christian era.