a particular period of time marked by distinctive features, events, etc.

The treaty ushered in an epoch of peace and good will.

the beginning of a distinctive period in the history of anything

The splitting of the atom marked an epoch in scientific discovery.

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.

Geology . any of several divisions of a geologic period during which a geologic series is formed. Compare age ( def. 12 ) .

Astronomy .

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.

the mean longitude of a planet as seen from the sun at such an instant or date.

Physics . the displacement from zero at zero time of a body undergoing simple harmonic motion.

noun

age , date , era , span , [[timenotes:epoch applies to the beginning of a new period marked by radical changes and new developments - while era applies to the entire period; age denotes a period identified with some dominant personality or characteristic and period pertains to any portion of time]] , day , period , time , event , interval