nutation
/njuːˈteɪʃən/noun
mass noun
1- a periodic variation in the inclination of the axis of a rotating object（旋转物体轴心的）倾斜度周期性变化。
1.1
- Astronomy a periodic oscillation of the earth's axis which causes the precession of the poles to follow a wavy rather than a circular path【天文】章动。
1.2
- Botany the circular swaying movement of the tip of a growing shoot【植】外卷, 回转, 转头（运动）。
词源
early 17th cent. (denoting nodding of the head)： from Latin nutatio（n-）， from nutare 'to nod'.