The Collaborative International Dictionary of English v.0.48:

Stun \Stun\, n.
   The condition of being stunned.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

            One hung a poleax at his saddlebow,
            And one a heavy mace to stun the foe. --Dryden.
      [1913 Webster]

   2. To dull or deaden the sensibility of; to overcome;
      especially, to overpower one's sense of hearing.
      [1913 Webster]

            And stunned him with the music of the spheres.
                                                  --Pope.
      [1913 Webster]

   3. To astonish; to overpower; to bewilder.
      [1913 Webster]

            William was quite stunned at my discourse. --De Foe.
      [1913 Webster]

WordNet (r) 3.0 (2006):

stun
    v 1: make senseless or dizzy by or as if by a blow; "stun fish"
         [syn: stun, stupefy]
    2: hit something or somebody as if with a sandbag [syn:
       sandbag, stun]
    3: overcome as with astonishment or disbelief; "The news stunned
       her" [syn: stun, bedaze, daze]