Source : Webster's Revised Unabridged Dictionary (1913)

Stun \Stun\, v. t. [imp. & p. p. {Stunned}; p. pr. & vb. n.
   {Stunning}.] [OE. stonien, stownien; either fr. AS. stunian
   to resound (cf. D. stenen to groan, G. st["o]hnen, Icel.
   stynja, Gr. ?, Skr. stan to thunder, and E. thunder), or from
   the same source as E. astonish. [root]168.]
   1. To make senseless or dizzy by violence; to render
      senseless by a blow, as on the head.

            One hung a poleax at his saddlebow, And one a heavy
            mace to stun the foe.                 --Dryden.

   2. To dull or deaden the sensibility of; to overcome;
      especially, to overpower one's sense of hearing.

            And stunned him with the music of the spheres.
                                                  --Pope.

   3. To astonish; to overpower; to bewilder.

            William was quite stunned at my discourse. --De Foe.

Stun \Stun\, n.
   The condition of being stunned.

Source : WordNet®

stun
     v 1: make senseless or dizzy by or as if by a blow; "stun fish"
          [syn: {stupefy}]
     2: surprise greatly; knock someone's socks off; "I was floored
        when I heard that I was promoted" [syn: {shock}, {floor},
        {ball over}, {blow out of the water}, {take aback}]
     3: hit something or somebody as if with a sandbag [syn: {sandbag}]
     4: overcome as with astonishment or disbelief; "The news
        stunned her" [syn: {bedaze}, {daze}]
     [also: {stunning}, {stunned}]