Longman Dictionary of Contemporary English
Douglas Harper's Etymology Dictionary
"abuse someone verbally," 1941, probably ultimately from noun phrase bad mouth (1835), in Black English, "a curse, spell," translating an idiom found in African and West Indian languages. Related: Bad-mouthed; bad-mouthing.
Wiktionary
vb. (alternative spelling of badmouth English)
Usage examples of "bad-mouth".
The thing is, you know that as soon as you leave town they are going to bad-mouth you rotten.
If I bad-mouthed Big Jim elsewhere then, please, let it lie, because right now.
Since what their cameyes taped was admissable evidence, any criminal who bad-mouthed the government was usually charged with other crimes of dissent, imaginary or not.
All the other women, no one admitted that they'd ever cursed a word in their lives or bad-mouthed their husbands.
What I want to do now is go over those reports again and have MAX correlate just how many times anyone said the murdered women might have even occasionally cursed or even bad-mouthed their husbands just one time.
What they couldn't have been certain about was that the women also bad-mouthed their husbands.
The six women you purified in San Francisco, all of them cursed and bad-mouthed their husbands?
No way was she going to wave them in the face of the lascivious, arrogant, bad-mouthed man who had been the torment of her life for four long undergraduate years at Stonewall.
You bad-mouthed me, told her not to hire me, then spread it everywhere to embarrass me.
She terrorized everyone who worked for her, bad-mouthed her friends behind their backs, and let the world believe a hardworking English boy—who adored her to pieces, mind you—was little better than a gigolo.
It wouldn't do to have her bad-mouthing him to her little circle of friends.
Partly it's because of the jobs you snatched up and the way our ma bad-mouths him and slaps him around for not grabbing them first.
So far, he'd mostly been interested in sucking down rippers and bad-mouthing his recent ex-wife.