noun

1. the beginning of a new and important period in the history of anything the first earth satellite marked a new epoch in the study of the universe
2. a period of time considered in terms of noteworthy and characteristic events, developments, persons, etc. an epoch of social revolution
3. a point in time or a precise date
4. Astron. the time at which observations are made, as of the positions of planets or stars
5. Geol. a subdivision of a period in geologic time corresponding to the rock strata of a series ()

Etymology: ML epocha < Gr epochē, a check, cessation < epechein, to hold in, check < epi-, upon + echein, to hold: see scheme