precession

Meanings

1. 1
   noun

   the slow conical motion of a spinning body's rotation axis, usually caused by an external torque

   The spinning top's axis traced a slow circle because of precession.

2. 2
   noun

   astronomy: a gradual change in the orientation of an astronomical body's rotation axis or orbit

   Earth's axial precession slowly changes the position of the celestial poles.

From Medieval Latin praecessio ("a going before"), from Latin praecedere ("to go before, precede"). The astronomical term first referred to the equinoxes' apparent westward "preceding" along the ecliptic; mechanics later applied it to a spinning axis's slow gyration.

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