Source : Webster's Revised Unabridged Dictionary (1913)

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

            No puissant stroke his senses once astound.
                                                  --Fairfax.

   2. To astonish; to strike with amazement; to confound with
      wonder, surprise, or fear.

            These thoughts may startle well, but not astound The
            virtuous mind.                        --Milton.

Astounding \As*tound"ing\, a.
   Of a nature to astound; astonishing; amazing; as, an
   astounding force, statement, or fact. -- {As*tound"ing*ly},
   adv.

Source : WordNet®

astounding
     adj 1: bewildering or striking dumb with wonder [syn: {dumbfounding},
             {dumfounding}]
     2: so surprisingly impressive as to stun or overwhelm; "such an
        enormous response was astonishing"; "an astounding
        achievement"; "the amount of money required was
        staggering"; "suffered a staggering defeat"; "the figure
        inside the boucle dress was stupefying" [syn: {astonishing},
         {staggering}, {stupefying}]