Synonyms for Incredible (same or very similar meaning)
WordNet sense 1 (too improbable to admit of belief):
improbable, marvelousWordNet sense 2 (barely credible):
fabulousWordNet sense 3 (bewildering or striking dumb with wonder):
astoundingWordNet sense 4 (beyond belief or understanding):
unbelievableFrom the ODE community, based on WordNetadd/edit