Insanity

n. madness, craziness, lunacy, mental derangement; extreme foolishness, foolhardiness

Insanity, or madness, is a general popular and legal term defining behaviour influenced by mental instability. It is defined by the Merriam-Webster dictionary as a deranged state of the mind or lack of understanding. Today it is most commonly encountered as an informal term or in the narrow legal context of the insanity defense, and in the medical profession, the term is now avoided in favour of specific diagnoses of mental illness as schizophrenia and other psychotic disorders.
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Insanity /in·san·i·ty/ a legal term for mental illness of such degree that the individual is not responsible for his or her acts. [more]Insanity - Community and Resources

Noun
1. relatively permanent disorder of the mind
(antonym) sanity, saneness
(hypernym) mental illness, mental disease, psychopathy
(hyponym) lunacy, madness, insaneness

(n.)
The state of being insane; unsoundness or derangement of mind; madness; lunacy.
  

(n.)
Such a mental condition, as, either from the existence of delusions, or from incapacity to distinguish between right and wrong, with regard to any matter under action, does away with individual responsibility.