Improbable
ahd-5
adjective.
Unlikely to take place or be true.
The Century Dictionary and Cyclopedia
Not probable; not likely to be true; not to be expected under the circumstances of the case.
the GNU version of the Collaborative International Dictionary of English
adjective.
Not probable; unlikely to be true; not to be expected under the circumstances or in the usual course of events.
Wiktionary, Creative Commons Attribution/Share-Alike License
adjective.
Not likely to be true.
adjective.
Not likely to happen.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adjective.
having a probability too low to inspire belief
adjective.
too improbable to admit of belief
adjective.
not likely to be true or to occur or to have occurred