Definition of: epoch

(ep′ək, Brit, ē′pok) noun
1. A point in the onward course of history from which succeeding years are counted: Atomic energy marks an epoch in history.
2. An interval of time or a series of years, regarded as a whole, memorable for extraordinary events and far–reaching results; any definite period of history.
3. Geol. A minor subdivision of time; a time interval less than a period: the Pleistocene epoch. See chart under GEOLOGY.
4. Astron. A moment of time when a planet reaches a certain known position with reference to the sun. [<Gk. epochē a stoppage, point of time <epi- upon + echein have]