nutation

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The act or an instance of nodding the head.
2. n. A wobble in a spinning gyroscope or other rotating body.
3. n. Astronomy A small periodic motion of the celestial pole of the earth with respect to the pole of the ecliptic.
4. n. Botany A slight curving or circular movement in a stem, as of a twining plant, caused by irregular growth rates of different parts.

Century Dictionary and Cyclopedia

1. n. A nodding.
2. n. In pathology, a constant nodding or involuntary shaking of the head.
3. n. In astronomy, a small subordinate gyratory movement of the earth's axis, in virtue of which, if it subsisted alone, the pole would describe among the stars, in a period of about nineteen years, a minute ellipse, having its longer axis directed toward the pole of the ecliptic, and the shorter, of course, at right angles to it. The consequence of this real motion of the pole is an apparent approach and recession of all the stars in the heavens to the pole in the same period; and the same cause will give rise to a small alternate advance and recession of the equinoctial points, by which both the longitudes and the right ascensions of the stars will be also alternately increased or diminished. This nutation, however, is combined with another motion—namely, the precession of the equinoxes—and in virtue of the two motions the path which the pole describes is neither an ellipse nor a circle, but a gently undulated ring; and these undulations constitute each of them a nutation of the earth's axis. Both these motions and their combined effect arise from the same physical cause—namely, the action of the sun and moon upon the protuberant mass at the earth's equator. See precession.
4. n. In botany, same as circumnutation.

Wiktionary

1. n. physics a bobbing motion that accompanies the precession of a spinning rigid body
2. n. a nodding motion (of the head etc.)
3. n. astronomy any of several irregularities in the precession of the equinoxes caused by varying torque applied to the Earth by the Sun and the Moon
4. n. botany the circular motion of the tip of a growing shoot

GNU Webster's 1913

1. n. The act of nodding.
2. n. (Astron.) A very small libratory motion of the earth's axis, by which its inclination to the plane of the ecliptic is constantly varying by a small amount.
3. n. The motion of a flower in following the apparent movement of the sun, from the east in the morning to the west in the evening.
4. n. Circumnutation.

WordNet 3.0

1. n. uncontrolled nodding