From The Collaborative International Dictionary of English v.0.48 [gcide]:
Epoch \Ep"och\ ([e^]p"[o^]k or [=e]"p[o^]k; 277), n. [LL.
epocha, Gr. 'epochh` check, stop, an epoch of a star, an
historical epoch, fr. 'epe`chein to hold on, check; 'epi`
upon + 'e`chein 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.
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In divers ages, . . . divers epochs of time were
used. --Usher.
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Great epochs and crises in the kingdom of God.
--Trench.
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The acquittal of the bishops was not the only event
which makes the 30th of June, 1688, a great epoch in
history. --Macaulay.
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Note: Epochs mark the beginning of new historical periods,
and dates are often numbered from them.
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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.
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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.
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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.
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The long geological epoch which stored up the vast
coal measures. --J. C.
Shairp.
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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.
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The capture of Constantinople is an epoch in the
history of Mahometanism; but the flight of
Mahomet is its era. --C. J. Smith.
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From WordNet (r) 3.0 (2006) [wn]:
epoch
n 1: a period marked by distinctive character or reckoned from a
fixed point or event [syn: {era}, {epoch}]
2: (astronomy) an arbitrarily fixed date that is the point in
time relative to which information (as coordinates of a
celestial body) is recorded [syn: {epoch}, {date of
reference}]
3: a unit of geological time that is a subdivision of a period
and is itself divided into ages
From The Jargon File (version 4.4.7, 29 Dec 2003) [jargon]:
epoch
n.
[Unix: prob.: 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 U.S. 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}. Microsoft
Windows, on the other hand, has an epoch problem every 49.7 days ? but this
is seldom noticed as Windows is almost incapable of staying up continuously
for that long.
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