badmouth

UK: /ˈbædmaʊθ/

WordReference Random House Learner's Dictionary of American English © 2025

ˈbad-ˌmouth or ˈbadˌmouth, v. [ ~ + obj]

1. to criticize, often disloyally:
   disliked her boss, but never bad-mouthed him.

WordReference Random House Unabridged Dictionary of American English © 2025

bad-mouth  (bad′mouth′ or, sometimes, -mouᵺ′), v.t., -mouthed, -mouth•ing. 

1. [Slang.] to speak critically and often disloyally of;
   disparage:
   Why do you bad-mouth your family so much?
   Also, bad′mouth′. 

• 1935–40; origin, originally a curse, spell (the sense recorded in Gullah); compare Vai (Mande language of Liberia and Sierra Leone) dà n^yà mà curse, literally, bad mouth

bad′-mouth′er, n. 

Collins Concise English Dictionary © HarperCollins Publishers::

bad-mouth verb

1. (transitive) to speak unfavourably about