nutation
    n 1: uncontrolled nodding

Nutation \Nu*ta"tion\, n. [L. nutatio a nodding, fr. nutare to
   nod: cf. F. nutation.]
   1. The act of nodding.
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            So from the midmost the nutation spreads,
            Round and more round, o'er all the sea of heads.
                                                  --Pope.
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   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.
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   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.
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