insanity

noun, plural in·san·i·ties.

1. the condition of being insane; a derangement of the mind.
2. Law. such unsoundness of mind as frees one from legal responsibility, as for committing a crime, or as signals one’s lack of legal capacity, as for entering into a contractual agreement.
3. Psychiatry. (formerly) psychosis.
4. 1. extreme foolishness; folly; senselessness; foolhardiness: Trying to drive through that traffic would be pure insanity.
   2. a foolish or senseless action, policy, statement, etc.: We’ve heard decades of insanities in our political discourse.

noun plural -ties

1. relatively permanent disorder of the mind; state or condition of being insane
2. law a defect of reason as a result of mental illness, such that a defendant does not know what he or she is doing or that it is wrong
3. utter folly; stupidity

n.

1. Persistent mental disorder or derangement. Not in scientific use.
2. 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.
3. In most criminal jurisdictions, a degree of mental malfunctioning considered to be sufficient to relieve the accused of legal responsibility for the act committed.