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English word dumbass unsurprisingly comes from English dumb and ass. It originated in the United States in 1970–75
ass (English)
The rear part of a person or animal. A donkey.
dumb (English)
(dated) To silence.. (transitive) To make stupid.. (transitive) To reduce the intellectual demands of.. (transitive) To represent as stupid. (dated) Silent; unaccompanied by words.. (dated) Unable to speak; lacking power of speech (kept in "deaf, dumb, and blind").. (figuratively) Pointless, foolish, lacking intellectual content or value.. (informal, pejorative, especially of a person) [...]
dumbass (English)
(US, vulgar, slang) A stupid or foolish person. Stupid, foolish.