a person who is notably stupid or lacking in good judgment.

Psychology . a person of borderline intelligence in a former classification of mental retardation, having an intelligence quotient of 50 to 69.

adjective

asinine , brainless , dense , dimwitted , doltish , dopey * , dumb , foolish , half-baked * , idiotic , ill-advised , imbecilic , inane , irresponsible , ludicrous , mindless , nonsensical , pointless , senseless , unintelligent , unthinking , absurd , harebrained , insane , lunatic , mad , preposterous , silly , softheaded , tomfool , unearthly , zany