nutation

n. [ L. nutatio a nodding, fr. nutare to nod: cf. F. nutation. ] 1. The act of nodding. [ 1913 Webster ]

So from the midmost the nutation spreads,
Round and more round, o'er all the sea of heads. Pope. [ 1913 Webster ]

2. (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. [ 1913 Webster ]

3. (Bot.) (a) 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. (b) Circumnutation. [ 1913 Webster ]