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[pree-sesh-uh n] /priˈsɛʃ ən/
the act or fact of preceding; precedence.
Mechanics. the motion of the rotation axis of a rigid body, as a spinning top, when a disturbing torque is applied while the body is rotating such that the rotation axis describes a cone, with the vertical through the vertex of the body as axis of the cone, and the motion of the rotating body is perpendicular to the direction of the torque.
  1. the slow, conical motion of the earth's axis of rotation, caused by the gravitational attraction of the sun and moon, and, to a smaller extent, of the planets, on the equatorial bulge of the earth.
  2. precession of the equinoxes.
Origin of precession
1300-50; < Late Latin praecessiōn- (stem of praecessiō) a going before, advance, equivalent to Latin praecess(us) (past participle of praecēdere to precede) + -iōn- -ion; see cession
Related forms
precessional, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for precession
Historical Examples
  • It is as much outside 97 our control as the precession of the equinoxes.

    Waiting for Daylight Henry Major Tomlinson
  • If the earth were a perfect sphere, precession would be inexplicable.

    The Story of the Heavens Robert Stawell Ball
  • In fact he had discovered the physical cause of that precession.

    Pioneers of Science Oliver Lodge
  • Of these the principal are devoted to the effect of precession.

    The Royal Observatory Greenwich

    E. Walter (Edwared Walter) Maunder
  • Its movement we see in the heavens in the precession of the equinoxes.

    Everyday Objects W. H. Davenport Adams
  • Making proper allowance for the precession of the equinoxes.

    Comets and Meteors Daniel Kirkwood
  • He knows about as much about mining as a hog does about the precession of the equinox.

    Shadow Mountain Dane Coolidge
  • If this rule is right, we see at once why precession takes place.

    Spinning Tops John Perry
  • Hurry on the precession, and the body rises in opposition to gravity.

    Spinning Tops John Perry
  • This precession continues until the roller and the shelf cease to touch.

    Spinning Tops John Perry
British Dictionary definitions for precession


the act of preceding
the motion of a spinning body, such as a top, gyroscope, or planet, in which it wobbles so that the axis of rotation sweeps out a cone
Derived Forms
precessional, adjective
precessionally, adverb
Word Origin
C16: from Late Latin praecessiō a going in advance, from Latin praecēdere to precede
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for precession

1590s, from Late Latin praecissionem (nominative praecissio) "a coming before," from past participle stem of Latin praecedere "to go before" (see precede). Originally used in reference to calculations of the equinoxes, which come slightly earlier each year.

Online Etymology Dictionary, © 2010 Douglas Harper
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precession in Science
  1. The rotational motion of the axis of a spinning body, such as the wobbling of a spinning top, caused by torque applied to the body along its axis of rotation.

  2. The motion of this kind made by the Earth's axis, caused mainly by the gravitational pull of the Sun, Moon, and other planets. The precession of Earth's axis has a period of nearly 25,800 years, during which time the reference points on the equatorial coordinate system (the celestial poles and celestial equator) will gradually shift their positions on the celestial sphere. ◇ The precession of the equinoxes is the slow westward shift of the autumnal and vernal equinoxes along the ecliptic, resulting from precession of the Earth's axis. See also nutation.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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