ep·och (ĕpək, ēpŏk′)
1. A particular period of history, especially one considered remarkable or noteworthy.
2. A unit of geologic time that is a division of a period.
3. Astronomy An instant in time that is arbitrarily selected as a point of reference for specification of celestial coordinates.
[Medieval Latin epocha, measure of time, from Greek epokhē, a point in time; see segh- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.