WordWeb Online

1. Bewildering or striking dumb with wonder
   - dumbfounding, dumfounding
    
2. So surprisingly impressive as to stun or overwhelm
   "an astounding achievement"
   - astonishing, staggering, stupefying

1. Affect with wonder
   "Your ability to speak six languages astounds me!"
   - amaze, astonish

See also: impressive, incredible, unbelievable

Type of: surprise

Encyclopedia: Astounding