Source : Webster's Revised Unabridged Dictionary (1913)

Nod \Nod\, n.
   1. A dropping or bending forward of the upper oart or top of
      anything.

            Like a drunken sailor on a mast, Ready with every
            nod to tumble down.                   --Shak.

   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.

            A look or a nod only ought to correct them [the
            children] when they do amiss.         --Locke.

            Nations obey my word and wait my nod. --Prior.

   {The land of Nod}, sleep.