Nutation

Part of speech: noun (n.)

1. The act of nodding. So from the midmost the nutation spreads, Round and more round, o'er all the sea of heads. Pope.

2. 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. 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. Circumnutation.