mental illness

American  

noun

• mental illnesses
  plural

1. any of the various forms of psychosis or severe neurosis.

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mental illness British  

noun

1. any of various disorders in which a person's thoughts, emotions, or behaviour are so abnormal as to cause suffering to himself, herself, or other people

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mental illness Scientific  

/ mĕn′tl /

1. Any of various psychiatric disorders or diseases, usually characterized by impairment of thought, mood, or behavior.

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Other Word Forms

Noun Inflected Forms

• mental illnesses
  plural

Etymology

Origin of mental illness

First recorded in 1960–65

Example Sentences

See Examples For:

mental illness

Prosecutors questioned the schizophrenia diagnosis and pointed out that suffering from mental illness is not the same as meeting the legal standard of insanity.

From Los Angeles Times ● Oct. 1, 2026

The defence did not have to prove her mental illness or lack of criminal responsibility.

From BBC ● Sep. 18, 2026

Don’t miss: ‘I currently give him $1,000 a month’: My grandson has severe mental illness.

From MarketWatch ● Sep. 14, 2026

Under Massachusetts law, there was no burden on Clancy to prove her mental illness and that she lacked criminal responsibility.

From BBC ● Sep. 9, 2026

The patients included those who suffered with epilepsy, mental illness, blindness, deafness, mental disabilities, and severe physical deformities.

From "Hitler Youth: Growing Up in Hitler's Shadow" by Susan Campbell Bartoletti

Related Words

• insanity
• mental disorder