re: What is the definition of insanity?

Merriam-Webster Dictionary: Insanity is defined as a severely disordered state of the mind usually occurring as a specific disorder. It also refers to law, specifically as a state of being mentally ill so severely that one cannot be held responsible for one's actions.

Oxford English Dictionary (OED): The OED describes insanity as the state of being seriously mentally ill; madness. It also notes its use in legal contexts to denote a degree of mental illness that relieves the sufferer of legal responsibility for their actions.

Cambridge Dictionary: This dictionary defines insanity as the condition of being seriously mentally ill; madness. It also mentions its use in informal situations to describe actions that are very foolish or unreasonable.

Collins English Dictionary: Insanity is defined as relatively permanent disorder of the mind; state or condition of being insane. It emphasizes on a legal definition as well, indicating a condition of such mental illness that a person cannot be held responsible for their actions.

American Heritage Dictionary: Defines insanity as a severe mental disorder, with or without organic damage, characterized by derangement of personality and loss of contact with reality and causing deterioration of normal social functioning.