dumbfounding

from WordNet (r) 3.0 (2006)

dumbfounding
    adj 1: bewildering or striking dumb with wonder [syn:
           {astounding}, {dumbfounding}, {dumfounding}]

from The Collaborative International Dictionary of English v.0.48

dumbfounding \dumbfounding\ adj.
   causing astonishment. [Narrower terms: {incredible (vs.
   credible), unbelievable}]

   Syn: astonishing, astounding, dumfounding.
        [WordNet 1.5]