The Collaborative International Dictionary of English v.0.48:

Astound \As*tound"\, v. t. [imp. & p. p. Astounded, [Obs.]
   Astound; p. pr. & vb. n. Astounding.] [See Astound, a.]
   1. To stun; to stupefy.
      [1913 Webster]

            No puissant stroke his senses once astound.
                                                  --Fairfax.
      [1913 Webster]

   2. To astonish; to strike with amazement; to confound with
      wonder, surprise, or fear.
      [1913 Webster]

            These thoughts may startle well, but not astound
            The virtuous mind.                    --Milton.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

astounded \astounded\ adj.
   1. struck with an intense and usually sudden surprise
      sufficient to produce wonder or perplexity

   Syn: amazed, astonied, astonished, dumbfounded,
        flabbergasted, stunned, stupefied, thunderstruck
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

astounded
    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, stunned]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "astounded":
   agape, aghast, agog, all agog, amazed, appalled, ashen, astonished,
   at gaze, awed, awestricken, awestruck, beguiled, bewildered,
   bewitched, blanched, breathless, captivated, confounded, cowed,
   deadly pale, dumbfounded, dumbstruck, enchanted, enraptured,
   enravished, enthralled, entranced, fascinated, flabbergasted,
   frozen, gaping, gauping, gazing, gray with fear, horrified,
   horror-struck, hypnotized, in awe, in awe of, intimidated,
   lost in wonder, marveling, mesmerized, open-eyed, openmouthed,
   overwhelmed, pale as death, pallid, paralyzed, petrified, popeyed,
   puzzled, rapt in wonder, scared stiff, scared to death, spellbound,
   staggered, staring, stunned, stupefied, surprised, terrified,
   terror-crazed, terror-haunted, terror-ridden, terror-riven,
   terror-shaken, terror-smitten, terror-struck, terror-troubled,
   thunderstruck, under a charm, undone, unmanned, unnerved, unstrung,
   wide-eyed, wonder-struck, wondering