Lunacy (noun)

1. The state of being insane or mentally ill.
2. Extreme foolishness or irrationality.

Origin:

The term "lunacy" comes from the latin word luna which means moon. it was used to describe the belief that the full moon caused mental illness.

Examples:

1. The lawyer pleaded not guilty by reason of lunacy.
2. The patient's lunacy made it difficult for the doctor to communicate with them.
3. The politician's proposal was met with accusations of lunacy.
4. The company's decision to invest in a failing industry was seen as a sign of lunacy.
5. The behavior of the crowd was described as a lunacy.