Precession

noun
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.

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.
precession of the equinoxes.

noun
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
precession
(prē-sěsh’ən)

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.

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.