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.

Source : WordNet®

stunned
     adj 1: filled with the emotional impact of overwhelming surprise or
            shock; "an amazed audience gave the magician a
            standing ovation"; "I stood enthralled, astonished by
            the vastness and majesty of the cathedral"; "astounded
            viewers wept at the pictures from the Oklahoma City
            bombing"; "stood in stunned silence"; "stunned
            scientists found not one but at least three viruses"
            [syn: {amazed}, {astonied}, {astonished}, {astounded}]
     2: knocked unconscious by a heavy blow [syn: {knocked out(p)},
        {kayoed}, {KO'd}, {out(p)}]
     3: in a state of mental numbness especially as resulting from
        shock; "he had a dazed expression on his face"; "lay
        semiconscious, stunned (or stupefied) by the blow"; "was
        stupid from fatigue" [syn: {dazed}, {stupefied}, {stupid(p)}]

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}]

stunned
     See {stun}