the condition of being insane; a derangement of the mind. Synonyms: dementia, lunacy, madness, craziness, mania, aberration.
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.
Psychiatry. (formerly) psychosis.
extreme foolishness; folly; senselessness; foolhardiness: Trying to drive through that traffic would be pure insanity. a foolish or senseless action, policy, statement, etc.: We've heard decades of insanities in our political discourse.
relatively permanent disorder of the mind; state or condition of being insane