The state of being insane; unsoundness or derangement of mind; madness; lunacy.
- Mental illness or derangement. No longer in scientific use.
- Law Unsoundness of mind sufficient in the judgment of a civil court to render a person unfit to maintain a contractual or other legal relationship or to warrant commitment to a mental health facility.
- Law In most criminal jurisdictions, a degree of mental malfunctioning sufficient to relieve the accused of legal responsibility for the act committed.
- Extreme foolishness; folly.
- Something that is extremely foolish.