epoch

• epocha [17th–19th c.]

From 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, “I hold in, check”), from ἐπι- (epi-, “upon”) + ἔχω (ékhō, “I have, hold”).

• (UK) IPA^(key): /ˈiːpɒk/, /ˈɛpək/

• Audio (Southern England)

  (file)

• Audio (Southern England)

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• (US) IPA^(key): /ˈɛp.ək/, /ˈɛpˌɑk/, /ˈiˌpɑk/, /ˈeɪˌpɑk/

• Audio (US)

  (file)

• Rhymes: -ɛpək, -eɪpɑk

epoch (plural epochs)

1. A particular period of history, or of a person's life, especially one considered noteworthy or remarkable.

   Synonyms: age, (only in general usage) era

   • 1834, L[etitia] E[lizabeth] L[andon], chapter XVII, in Francesca Carrara. […], volume I, London: Richard Bentley, […], (successor to Henry Colburn), →OCLC, page 198:

     I grew bitter in my words—I believed the worst of everyone; nay, I sometimes doubted the affection of my kind, my indulgent parents. But let me hastily pass over this vain and profitless epoch,—the fierce tempest, and the weary calm, were but the appointed means by which I reached the harbour of faith and rest.

   • 1924, F. Hopman, transl., The Waning of the Middle Ages, translation of Herfsttij der Middeleeuwen by Johan Huizinga:

     And it occasionally happens that a period in which one had, hitherto, been mainly looking for the coming to birth of new things, suddenly reveals itself as an epoch of fading and decay.

2. A notable event which marks the beginning of such a period.
3. (chronology, astronomy, computing) A specific instant in time, chosen as the point of reference or zero value of a system that involves identifying instants of time.

   Coordinate term: (cartography, engineering) datum

   UNIX epoch; J2000 epoch

   • 2000, Carl D. Murray, Stanley F. Dermott, Solar System Dynamics‎, Cambridge University Press, →ISBN:

     Appendix A gives formulae for the calculation of the orbital elements of the planets at any time referred to the mean ecliptic and equinox of the epoch of noon on 1st January 2000; this is called the J2000 epoch.

   • 2016, Preston Miller, Chapin Bryce, Learning Python for Forensics, Packt Publishing Ltd, →ISBN, page 281:

     There are two major epoch times associated with most timestamps: 1970-01-01 00:00:00 and 1601-01-01 00:00:00. The first, starting in 1970, is traditionally referred to as POSIX time as it is a common timestamp in UNIX and UNIX-like systems.

   • 2022, Tomasz Lelek, Jon Skeet, Software Mistakes and Tradeoffs: How to Make Good Programming Decisions, Simon and Schuster, →ISBN, page 155:

     The .NET epoch is midnight at the start of January 1st, AD 1, although that's AD 1 in a proleptic Gregorian calendar, which refers to even more complexity we haven't talked about yet.

4. (geology) A geochronologic unit of hundreds of thousands to millions of years; a subdivision of a period, and subdivided into ages (or sometimes subepochs).
   • 1881, Alfred Russel Wallace, chapter VIII, in Island Life:

     Now during the time of the glacial epoch the greatest distance of the sun in winter was 98¼ millions of miles, whereas it is now, in winter, only 91½ millions of miles, the mean distance being taken as 93 million miles.

   • 2012 January, Donald Worster, “A Drier and Hotter Future”, in American Scientist‎, volume 100, number 1, archived from the original on 26 January 2012, page 70:

     Phoenix and Lubbock are both caught in severe drought, and it is going to get much worse. We may see many such [dust] storms in the decades ahead, along with species extinctions, radical disturbance of ecosystems, and intensified social conflict over land and water. Welcome to the Anthropocene, the epoch when humans have become a major geological and climatic force.

5. (machine learning) One complete presentation of the training data set to an iterative machine learning algorithm.

   Synonym: generation

   The neural network was trained over 500 epochs.

   • 2021, Joe Papa, PyTorch Pocket Reference, O'Reilly Media, →ISBN:

     For now, let's test and evaluate our GAN by comparing the results from the first epoch with the generated images from the last epoch.

• epochal
• epoche, epoché
• epochless

epoch (third-person singular simple present epochs, present participle epoching, simple past and past participle epoched)

1. (sciences, transitive) To divide (data) into segments by time period.
   • 2015 July 6, “Stronger Neural Modulation by Visual Motion Intensity in Autism Spectrum Disorders”, in PLOS ONE‎, →DOI:

     The continuous data were epoched into segments of 1500 ms (starting 500 ms before visual stimulus onset), time-locked to stimulus onset (0 ms) and sorted according to experimental conditions.

• “epoch”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.
• “epoch”, in The Century Dictionary […], New York, N.Y.: The Century Co., 1911, →OCLC.
• “epoch”, in OneLook Dictionary Search.

• Poche, chope, poché