mental illness. 1. A disorder in thought or mood so substantial that it impairs judgment, behavior, perceptions of reality, or the ability to cope with the ordinary demands of life. [Cases: Mental Health 3. C.J.S. Insane PersonsĀ§Ā§ 2, 6.] 2. Mental disease that is severe enough to necessitate care and treatment for the afflicted person’s own welfare or the welfare of others in the community.

[Blacks Law 8th]