Past tense of badmouth; spoke negatively or critically about someone, often unfairly or in their absence.
From 'bad' + 'mouth', literally 'to speak badly from one's mouth.' American slang from mid-1900s, combining Germanic 'bad' with common body-part verb construction (mouth, hand, face).
English loves combining 'bad' with body parts to create verbs—badmouth, bad-eye, bad-hand—but only 'badmouth' stuck in everyday speech, probably because talking badly is the most common offense we actually witness!
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