1. a particular period of time marked by distinctive features, events, etc.
2. the beginning of a distinctive period in the history of anything; start of an era.
3. a point of time distinguished by a particular event or state of affairs; a memorable date.
4. an extremely important, significant, or influential event.
5. Geology: any of several divisions of a geologic period during which a geologic series is formed.
6. Astronomy: a) an arbitrarily fixed instant of time or date, usually the beginning of a century or half century, used as a reference in giving the elements of a planetary orbit or the like. b) the mean longitude of a planet as seen from the sun at such an instant or date.
Etymology: Neo-Latin epocha < Greek epochḗ - pause, check, fixed time.