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slang A person who is not able to speak clearly or properly. Often used humorously or hyperbolically. Sorry, I'm such a mushmouth today—I didn't sleep properly last night, and I'm finding it hard to get my words out the right way. I was kind of a mushmouth as a kid because of a slight speech impediment.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
n. a person who does not or cannot speak clearly. How can a mushmouth like that get a job reading news on network television?
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.