The Collaborative International Dictionary of English v.0.48:

Nod \Nod\ (n[o^]d), n.
   1. A dropping or bending forward of the upper part or top of
      anything.
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            Like a drunken sailor on a mast,
            Ready with every nod to tumble down.  --Shak.
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   2. A quick or slight downward or forward motion of the head,
      in assent, in familiar salutation, in drowsiness, or in
      giving a signal, or a command; as, a nod of approval.
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            A look or a nod only ought to correct them [the
            children] when they do amiss.         --Locke.
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            Nations obey my word and wait my nod. --Prior.
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   The land of Nod, sleep.
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