Meaning

noun a period marked by distinctive character or reckoned from a fixed point or event

noun (astronomy) an arbitrarily fixed date that is the point in time relative to which information (as coordinates of a celestial body) is recorded

noun a unit of geological time that is a subdivision of a period and is itself divided into ages

originFrom Medieval Latin epocha, from Ancient Greek ἐποχή (epokhḗ, “a check, cessation, stop, pause, epoch of a star, i.e., the point at which it seems to halt after reaching the highest, and generally the place of a star; hence, a historical epoch”), from ἐπέχω (epékhō, “to hold in, check”), from ἐπι- (epi-, “upon”) + ἔχω (ékhō, “to have, hold”). Doublet of epoche.

Etymology from Wiktionary, CC BY-SA 3.0