Source : Webster's Revised Unabridged Dictionary (1913)

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.

   2. To signify by a nod; as, to nod approbation.

   3. To cause to bend. [Poetic]

            By every wind that nods the mountain pine. --Keats.

Nodding \Nod"ding\, a.
   Curved so that the apex hangs down; having the top bent
   downward.

Source : WordNet®

nod
     n 1: a sign of assent or salutation or command
     2: the act of nodding the head
     [also: {nodding}, {nodded}]

nodding
     adj : having branches or flower heads that bend downward; "nodding
           daffodils"; "the pendulous branches of a weeping
           willow"; "lilacs with drooping panicles of fragrant
           flowers" [syn: {cernuous}, {drooping}, {pendulous}]

nod
     v 1: express or signify by nodding; "He nodded his approval"
     2: lower and raise the head, as to indicate assent or agreement
        or confirmation; "The teacher nodded when the student gave
        the right answer"
     3: let the head fall forward through drowsiness; "The old man
        was nodding in his chair"
     4: sway gently back and forth, as is in a nodding motion; "the
        flowers were nodding in the breeze"
     5: be almost asleep; "The old man sat nodding by the fireplace"
     [also: {nodding}, {nodded}]

nodding
     See {nod}