<p><strong>Noun</strong></p><ul><li>The act or fact of preceding; precedence.</li><li>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 the axis of the cone, and the motion of the rotating body is perpendicular to the direction of the torque.</li><li>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.</li></ul>