from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Not to be believed; incredible: unbelievable luck.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Not to be believed.
- adj. Incredible; so surprising it is almost unable to believe.
- adj. Implausible or improbable.
from The Century Dictionary and Cyclopedia
- Not to be believed; incredible.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adj. having a probability too low to inspire belief
- adj. beyond belief or understanding
From un- + believe + -able. (Wiktionary)