[pree-sesh-uh n]
See more synonyms for precession on
  1. the act or fact of preceding; precedence.
  2. 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.
  3. Astronomy.
    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 formspre·ces·sion·al, adjective Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for precession

Historical Examples of precession

  • 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.

  • 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

British Dictionary definitions for precession


  1. the act of preceding
  2. See precession of the equinoxes
  3. 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 Formsprecessional, adjectiveprecessionally, adverb

Word Origin for precession

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

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

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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.