imbecile

A person with limited mental capacity who can perform tasks and think only like a young child, in medical circles meaning a person who lacks the capacity to develop beyond the mental age of a normal five- to seven-year-old child.obsolete

• It is an offence for a man to have unlawful sexual intercourse with a woman whom he knows to be an idiot or imbecile.

A fool, an idiot.derogatory

• VLADIMIR: Because he wouldn't save them. / ESTRAGON: From hell? / VLADIMIR: Imbecile! From death.
• “A rat picked up a drink can and threw it at me?” yelled Mr Big. “A big rat, guv’nor? One of them super-rats?” suggested Thumbs. “It landed on my head, you imbecile!”

Destitute of strength, whether of body or mind; feeble; impotent; especially, mentally weak.dated

• hospitals for the imbecile and insane