Not true or logically valid; fallacious: an unsound conclusion. (adjective)
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 "unsound" in a sentence
"The parliament cited the pontiff, and, when he failed to appear, loyally declared his title unsound, and, under the lead of their first president (another"
"Those Congressionally created entities saw the fees being collected by the private entities, and the Congressionally created entities got ever more involved in unsound lending pratices."
"I find the majority's reasoning more than "unsound" - it's simply wrong and actually has the potential to feed into the very prejudice they worry about."