a. Unsoundness of mind sufficient to render a person unfit to maintain a contractual or other legal relationship or sufficient to warrant commitment to a mental health facility.

b. Incapacity to form the criminal intent necessary for legal responsibility, as when a mental disorder prevents a person from knowing the difference between right and wrong.

c. Incapacity because of a mental disorder to participate adequately as a defendant in criminal proceedings or to understand the imposition of a criminal punishment, particularly the death penalty.

a. Extreme foolishness or irrationality: "The insanity of sending troops into Russia when European peace looked imminent horrified him" (Mary V. Dearborn).