The Collaborative International Dictionary of English v.0.48:

Whiplash \Whip"lash`\, n.
   1. The lash of a whip, -- usually made of thongs of leather,
      or of cords, braided or twisted.
      [1913 Webster]

   2. a sudden change of direction, resembling the motion of the
      tip of a whip when it is cracked.
      [PJC]

   3. a stinging psychological effect reminiscent of being stung
      by a whip.
      [PJC]

   4. a whiplash injury.
      [PJC]

WordNet (r) 3.0 (2006):

whiplash
    n 1: an injury to the neck (the cervical vertebrae) resulting
         from rapid acceleration or deceleration (as in an
         automobile accident) [syn: whiplash, whiplash injury]
    2: a quick blow delivered with a whip or whiplike object; "the
       whip raised a red welt" [syn: whip, lash, whiplash]