epoch

noun

1. a particular period of time marked by distinctive features, events, etc.: The treaty ushered in an epoch of peace and good will.
2. the beginning of a distinctive period in the history of anything: The splitting of the atom marked an epoch in scientific discovery.
3. a point of time distinguished by a particular event or state of affairs; a memorable date: His coming of age was an epoch in his life.
4. Geology. any of several divisions of a geologic period during which a geologic series is formed.Compare age(def 12).
5. Astronomy.
   1. 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.
   2. the mean longitude of a planet as seen from the sun at such an instant or date.
6. Physics. the displacement from zero at zero time of a body undergoing simple harmonic motion.

noun

1. a point in time beginning a new or distinctive periodthe invention of nuclear weapons marked an epoch in the history of warfare
2. a long period of time marked by some predominant or typical characteristic; era
3. astronomy a precise date to which information, such as coordinates, relating to a celestial body is referred
4. geology a unit of geological time within a period during which a series of rocks is formedthe Pleistocene epoch
5. physics the displacement of an oscillating or vibrating body at zero time

1. The shortest division of geologic time. An epoch is a subdivision of a period.