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mentally ill

American

adjective

having a mental illness.

noun

(used with a plural verb)

Usually the mentally ill mentally ill persons collectively.

Etymology

Origin of mentally ill

First recorded in 1935–40

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

She’s not only coaching the mentally ill Freddie but she’s also his romantic partner.

From Los Angeles Times • Apr. 22, 2026

Wiseman caused instant controversy with his first film, "Titicut Follies," which remains one of his most famous documentaries, shot in 1967 and capturing the bleak reality of an asylum for the mentally ill, Bridgewater.

From Barron's • Feb. 16, 2026

“The Housemaid” would be enjoyable enough had Seyfried only been giving a layered performance as a mentally ill housewife.

From Salon • Jan. 31, 2026

In 1811, Saxony’s king converted it into a model asylum for the mentally ill, and for many years it was.

From The Wall Street Journal • Nov. 24, 2025

Most overcrowded prisons don't have the capacity to provide care and treatment to the mentally ill.

From "Just Mercy" by Bryan Stevenson

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023