The Collaborative International Dictionary of English v.0.48:

Nod \Nod\, v. t. [imp. & p. p. Nodded; p. pr. & vb. n.
   Nodding.]
   1. To incline or bend, as the head or top; to make a motion
      of assent, of salutation, or of drowsiness with; as, to
      nod the head.
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   2. To signify by a nod; as, to nod approbation.
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   3. To cause to bend. [Poetic]
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            By every wind that nods the mountain pine. --Keats.
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