Source : Webster's Revised Unabridged Dictionary (1913)

Headshake \Head`shake`\, n.
   A significant shake of the head, commonly as a signal of
   denial. --Shak.

Source : WordNet®

headshake
     n : the act of turning your head left and right to signify
         denial or disbelief or bemusement; "I could tell from
         their headshakes that they didn't believe me" [syn: {headshaking}]