Idiot (noun)

1. A foolish or incompetent person.
2. A person with moderate to severe intellectual disability.

Origin:

Late 16th century (in the sense "professional fool or jester"): via latin from greek idiōtēs "person lacking professional skill", from idios "private, individual".

Examples:

1. He acted like an idiot and ruined the entire plan.
2. The genius scientist was considered an idiot by some due to his odd behavior.
3. Many people in the 19th century were institutionalized and labeled as idiots.
4. The new recruit proved to be an idiot and couldn't follow simple instructions.
5. People who think that way are just a bunch of idiots.