Source : Webster's Revised Unabridged Dictionary (1913)

Concussion \Con*cus"sion\, n. [L. concussio, fr. concutere,
   concussum, to shake violenty; con- + quatere to shake. See
   {Cashier}, {Quash}.]
   1. A shaking or agitation; a shock; caused by the collision
      of two bodies.

            It is believed that great ringing of bells, in
            populous cities, hath dissipated pestilent air;
            which may be from the concussion of the air.
                                                  --Bacon.

   2. (Med.) A condition of lowered functional activity, without
      visible structural change, produced in an organ by a
      shock, as by fall or blow; as, a concussion of the brain.

   3. (Civil Law) The unlawful forcing of another by threats of
      violence to yield up something of value.

            Then concussion, rapine, pilleries, Their catalogue
            of accusations fill.                  --Daniel.

   {Concussion fuse} (Mil.), one that is ignited by the
      concussion of the shell when it strikes.

   Syn: See {Shock}.

Source : WordNet®

concussion
     n 1: injury to the brain caused by a blow; usually resulting in
          loss of consciousness
     2: any violent blow