Insane (adjective)

1. Seriously mentally ill; having a completely disturbed state of mind.
2. Very foolish or dangerous.
3. Extremely enthusiastic or excited about something.

Origin:

Late middle english, from latin insanus, from in- + sanus healthy.

Examples:

1. The insane asylum was overcrowded with patients.
2. Her behavior was considered insane by those who saw it.
3. The idea of jumping from a plane without a parachute was insane.
4. She was insane about the new pop star and had all their albums and merchandise.
5. The fans were insane with excitement when the band took the stage.