|1.||an act or instance of nodding one's head, esp. involuntarily or spasmodically.|
|2.||Botany. spontaneous movements of plant parts during growth.|
|3.||Astronomy. the periodic oscillation observed in the precession of the earth's axis and the precession of the equinoxes.|
|4.||Mechanics. the variation of the inclination of the axis of a gyroscope to the vertical.|
Check-out these fant-nastic videos of dancing plants to back this up...