in|san|i|ty

in|san|i|ty «ihn SAN uh tee», noun, plural -ties.

1. a) the condition of being insane; mental disorder; madness. b) Law. any state of mental unsoundness, temporary or permanent, in which a person is not held responsible or considered competent: »

The accused murderer insisted he had fired the shot during a fit of temporary insanity.

2. a) extreme folly; complete lack of common sense: »

It is insanity to drive a car without any brakes.

b) an instance of this.