Slang. to speak critically and often disloyally of; disparage: Why do you bad-mouth your family so much?
Also, badmouth.
Origin: 1935–40; orig. a curse, spell (the sense recorded in Gullah); cf. Vai (Mande language of Liberia and Sierra Leone) dà nyà mà curse, lit., bad mouth
[bad-mouth or, sometimes, -mouth] 
