mental illness

noun

variants or mental disorder or less commonly mental disease

: any of a broad range of medical conditions (such as major depression, schizophrenia, obsessive compulsive disorder, or panic disorder) that are marked primarily by sufficient disorganization of personality, mind, or emotions to impair normal psychological functioning and cause marked distress or disability and that are typically associated with a disruption in normal thinking, feeling, mood, behavior, interpersonal interactions, or daily functioning

mentally ill adjective

Examples of mental illness in a Sentence

Recent Examples on the Web

Her case became a media sensation overnight, as the tragedy sparked widespread debate about postpartum mental illness and questions about what — and who — may have influenced her. —Emily Blackwood, PEOPLE, 7 Jan. 2026

There is a meaningful difference between the diagnosis and treatment of mental illness and the cultivation of mental health. —Scott Lomurray, Time, 6 Jan. 2026

Not only does Jolt provide an important window into the darker realities of mental illness, Scheinman’s willingness to share his story will no doubt help others who might be struggling. —Literary Hub, Literary Hub, 6 Jan. 2026

Doctors had determined Bigham was suffering from severe mental illness at the time of her daughter’s death. —Hannah Fry, Los Angeles Times, 6 Jan. 2026

Word History

First Known Use

1724, in the meaning defined above

Rhymes for mental illness

• stillness

Kids Definition

mental illness

noun

variants or mental disorder

: a medical condition that is marked by a mild to severe disturbance in the way a person thinks, feels, or acts and is usually accompanied by distress and problems functioning in daily activities or interacting with others

mentally ill adjective

Medical Definition

mental illness

noun

variants or mental disorder also mental disease

: any of a broad range of medical conditions (such as major depression, schizophrenia, obsessive compulsive disorder, or panic disorder) that are marked primarily by sufficient disorganization of personality, mind, or emotions to impair normal psychological functioning and cause marked distress or disability and that are typically associated with a disruption in normal thinking, feeling, mood, behavior, interpersonal interactions, or daily functioning

Some homeless families are also hindered by substance abuse and mental illness.

—Ellen L. Bassuk, Scientific American

Catatonia is usually an expression of mental disorders like bipolar disorder or schizophrenia, but it could also come from other medical problems, such as a brain tumor.

—Forrest Wickman, The Pittsburgh Post-Gazette

… mental diseases such as schizophrenia and manic depression may either involve more than one gene or may result from a complex mix of genetic predisposition and environmental rotten luck.

—Natalie Angier, The New York Times Book Review

mentally ill adjective

mentally ill patients

Mental health workers … perform a wide variety of therapeutic, supportive, and preventative functions for persons who are mentally ill and developmentally disabled.

—Barbara M. Swanson, Careers in Health Care

Legal Definition

mental illness

noun

mental ill·​ness

1

: mental disease

2

: a mental condition marked primarily by sufficient disorganization of personality, mind, and emotions to seriously impair the normal psychological and often social functioning of the individual

called also mental disorder