insanity

noun | in·san·i·ty

1. a : a disease, defect, or condition of the mind that renders one unable to understand the nature of a criminal act or the fact that it is wrong or to conform one's conduct to the requirements of the law being violated

   b : inability to understand and participate in legal proceedings brought against one : incompetence

   c : inability to understand the nature and purpose of a punishment (as the death penalty) to which one has been sentenced

   d : inability to understand the nature and consequences of one's acts (as making a will) or of events, matters, or proceedings in which one is involved — see also commitment, durham rule, irresistible impulse test, m'naghten test, not guilty by reason of insanity, substantial capacity test — compare capacity, competency, competent, diminished capacity, sanity

2. : the affirmative defense of having acted while insane