- a dunce; blockhead; dolt: Don't stand there like an imbecile. Open the door!
- (no longer in technical use; now considered offensive) a person of the second order in a former and discarded classification of intellectual disability, above the level of idiocy, having a mental age of seven or eight years and an intelligence quotient of 25 to 50.
- a person of very low intelligence (IQ of 25 to 50), usually capable only of guarding himself against danger and of performing simple mechanical tasks under supervision
- an extremely stupid person; dolt
- of or like an imbecile; mentally deficient; feeble-minded
- stupid or senseless