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.


  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

1610s, epocha, “point marking the start of a new period in time” (e.g. the founding of Rome, the birth of Christ, the Hegira), from Late Latin epocha, from Greek epokhe “stoppage, fixed point of time,” from epekhein “to pause, take up a position,” from epi “on” (see epi-) + ekhein “to hold” (see scheme (n.)). Transferred sense of “a period of time” is 1620s; geological usage (not a precise measurement) is from 1802.

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