WordWeb Online

1. Beyond belief or understanding
   "the book's plot is simply incredible"; "at incredible speed";
   - unbelievable
    
2. Surprising greatly
   - amazing, astonishing, jaw-dropping [informal]

See also: astounding, believability, breathtaking, credibility, credibleness, dumbfounding, dumfounding, fabulous, flimsy, heart-stopping, implausible, improbable, incredulous, marvellous [Brit, Cdn], marvelous [US], surprising, tall, unconvincing, undreamed, undreamed of, undreamt, undreamt of, unimagined, unthinkable

Encyclopedia: Incredible