[ in-san-i-tee ]
/ ɪnˈsæn ɪ ti /
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Definition of insanity

noun, plural in·san·i·ties.
(not in technical use as a medical diagnosis) the condition of being insane; a derangement of the mind.
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.
  1. extreme foolishness: 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.
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Origin of insanity

First recorded in 1580–90; from Latin insānitāt-, stem of insānitās “unsoundness of mind, insanity”; see origin at in-3, sanity
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

How to use insanity in a sentence

British Dictionary definitions for insanity

/ (ɪnˈsænɪtɪ) /

noun plural -ties
relatively permanent disorder of the mind; state or condition of being insane
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
utter folly; stupidity
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Medical definitions for insanity

[ ĭn-sănĭ-tē ]

Persistent mental disorder or derangement. Not in scientific use.
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.
In most criminal jurisdictions, a degree of mental malfunctioning considered to be sufficient to relieve the accused of legal responsibility for the act committed.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.