etymologeek.com dictionary
English word dumbass unsurprisingly comes from English dumb and ass. It originated in the United States in 1970–75.

Dumbass etymology history?

Dumbass detailed word origin explanation

Dictionary entryLanguageDefinition
ass English (eng) The rear part of a person or animal. A donkey.
dumb English (eng) (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 (eng) (US, vulgar, slang) A stupid or foolish person. Stupid, foolish.

Words with the same origin as dumbass

Descendants of your
yo you're
Descendants of dumb
dummy