Source : Webster's Revised Unabridged Dictionary (1913)

Epoch \Ep"och\ (?; 277), n. [LL. epocha, Gr. ? check, stop, an
   epoch of a star, an historical epoch, fr. ? to hold on,
   check; 'epi` upon + ? to have, hold; akin to Skr. sah to
   overpower, Goth. sigis victory, AS. sigor, sige, G. sieg: cf.
   F. ['e]poque. See {Scheme}.]
   1. A fixed point of time, established in history by the
      occurrence of some grand or remarkable event; a point of
      time marked by an event of great subsequent influence; as,
      the epoch of the creation; the birth of Christ was the
      epoch which gave rise to the Christian era.

            In divers ages, . . . divers epochs of time were
            used.                                 --Usher.

            Great epochs and crises in the kingdom of God.
                                                  --Trench.

            The acquittal of the bishops was not the only event
            which makes the 30th of June, 1688, a great epoch in
            history.                              --Macaulay.

   Note: Epochs mark the beginning of new historical periods,
         and dates are often numbered from them.

   2. A period of time, longer or shorter, remarkable for events
      of great subsequent influence; a memorable period; as, the
      epoch of maritime discovery, or of the Reformation. ``So
      vast an epoch of time.'' --F. Harrison.

            The influence of Chaucer continued to live even
            during the dreary interval which separates from one
            another two important epochs of our literary
            history.                              --A. W. Ward.

   3. (Geol.) A division of time characterized by the prevalence
      of similar conditions of the earth; commonly a minor
      division or part of a period.

            The long geological epoch which stored up the vast
            coal measures.                        --J. C.
                                                  Shairp.

   4. (Astron.)
      (a) The date at which a planet or comet has a longitude or
          position.
      (b) An arbitrary fixed date, for which the elements used
          in computing the place of a planet, or other heavenly
          body, at any other date, are given; as, the epoch of
          Mars; lunar elements for the epoch March 1st, 1860.

   Syn: Era; time; date; period; age.

   Usage: {Epoch}, {Era}. We speak of the era of the
          Reformation, when we think of it as a period, during
          which a new order of things prevailed; so also, the
          era of good feeling, etc. Had we been thinking of the
          time as marked by certain great events, or as a period
          in which great results were effected, we should have
          called the times when these events happened epochs,
          and the whole period an epoch.

                The capture of Constantinople is an epoch in the
                history of Mahometanism; but the flight of
                Mahomet is its era.               --C. J. Smith.

Source : WordNet®

epoch
     n 1: a period marked by distinctive character or reckoned from a
          fixed point or event [syn: {era}]
     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}]
     3: a unit of geological time

Source : Free On-Line Dictionary of Computing

epoch
     
        1. [Unix: probably from astronomical timekeeping] The time and
        date corresponding to 0 in an operating system's clock and
        timestamp values.  Under most Unix versions the epoch is
        00:00:00 GMT, January 1, 1970; under VMS, it's 00:00:00 of
        November 17, 1858 (base date of the US Naval Observatory's
        ephemerides); on a Macintosh, it's the midnight beginning
        January 1 1904.  System time is measured in seconds or {tick}s
        past the epoch.  Weird problems may ensue when the clock wraps
        around (see {wrap around}), which is not necessarily a rare
        event; on systems counting 10 ticks per second, a signed
        32-bit count of ticks is good only for 6.8 years.  The
        1-tick-per-second clock of Unix is good only until January 18,
        2038, assuming at least some software continues to consider it
        signed and that word lengths don't increase by then.  See also
        {wall time}.
     
        2. (Epoch) A version of {GNU Emacs} for the {X Window System}
        from {NCSA}.
     
        [{Jargon File}]