Informal. a dunce; blockhead; dolt: Don't stand there like an imbecile. Open the door!.
Psychology. (no longer in technical use; now considered offensive) a person of the second order in a former and discarded classification of mental retardation, above the level of idiocy, having a mental age of seven or eight years and an intelligence quotient of 25 to 50.
Informal. stupid; silly; absurd.
Usually Offensive. showing mental feebleness or incapacity.