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1. verb To speak negatively or unflatteringly about someone or something. Why are you always bad-mouthing Tiffany? You don't even know her that well!
2. noun One who says negative or unflattering things about someone or something. He's a real bad-mouth, so don't listen to anything he says about me!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
bad-mouth someone or something
to say negative things about someone or something. Mr. Smith was always bad-mouthing Mrs. Smith. They just didn't get along. John bad-mouths his car constantly because it is too small for him.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
Disparage or criticize unduly, malign, as in Why do you constantly bad mouth your colleagues? This term is believed to be of African origin, where the phrase bad mouth signifies a curse or evil spell. [1930s]
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
1. tv. to speak ill of someone or something. (see also dirty mouth, poor-mouth.) I wish you would stop bad-mouthing my car.
2. n. someone who speaks ill of someone or something. Harry is such a bad-mouth!
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.