epoch epoch /ˈiːpək/

noun

1. () A period marked by distinctive character or reckoned from a fixed point or event  ( epoch , era )
   a period marked by distinctive character or reckoned from a fixed point or event
     The invention of the internet marked a new epoch in human history.
   The invention of the internet marked a new epoch in human history.
   
2. A unit of geological time that is a subdivision of a period and is itself divided into ages  ( epoch )
   a unit of geological time that is a subdivision of a period and is itself divided into ages
   
3. (astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded  ( date of reference , epoch )
   (astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded