Difficult to foretell or foresee: unpredictable test results; unpredictable behavior. (adjective)
Something difficult or impossible to foretell or foresee.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "unpredictable" in a sentence
"In the regulated order of the modern state, the unpredictable is the ultimate aesthetic desire."
"He also called McCain "unpredictable," and questioned his knowledge on economic issues."
"Whether it will cause massive die outs and rising ocean levels or just an increase in unpredictable weather is not 100% clear."