ETYM Late Lat. epocha, Greek epoche check, stop, an epoch of a star, an historical epoch, from epechein to hold on, check.
(Homonym: epic).
1. A unit of geological time.
2. (Astronomy) The precise date that is the point of reference for which information (as coordinates of a celestial body) is referred; SYN. date of reference.
Subdivision of a geological period in the geological time scale. Epochs are sometimes given their own names (such as the Paleocene, Eocene, Oligocene, Miocene, and Pliocene epochs comprising the Tertiary period), or they are referred to as the late, early, or middle portions of a given period (as the Late Cretaceous or the Middle Triassic epoch).