dementia

noun

de·​men·​tia di-ˈmen(t)-shə 

-shē-ə

1

: a usually progressive condition (such as Alzheimer's disease) marked by the development of multiple cognitive deficits (such as memory impairment, aphasia, and the inability to plan and initiate complex behavior)

… dementia is diagnosed only when both memory and another cognitive function are each affected severely enough to interfere with a person's ability to carry out routine daily activities.

—The Journal of the American Medical Association

2

: madness, insanity

a fanaticism bordering on dementia

demential

di-ˈmen(t)-shəl 

-shē-əl

adjective

Synonyms of dementia

• schizophrenia
• insanity
• hysteria
• madness
• instability

Examples of dementia in a Sentence

This patient suffers from dementia.

a new study on age-related dementias

Recent Examples on the Web

One 2020 study of more than 63,000 adults found that those who retired at age 66 or older had about a 66 percent lower risk of dementia after a follow-up 24-year period compared to those who retired younger. — Richard Sima, Washington Post, 7 Nov. 2026

This movie about consent and dementia — and ultimately, far much more — hinges on a questionable act that provokes a hasty emotional reaction. — Los Angeles Times, 6 Nov. 2026

Meghan’s 82-year-old father has reportedly been transferred in recent days to a facility in Florida that specializes in caring for people with dementia, according to The Sun. — Stefania Conrieri, Vanity Fair, 6 Nov. 2026

Caregivers for dementia patients, whether family members at home or employees in an institution, can face daily challenges from residents who may be uncooperative or agitated, but advocates emphasize that caregivers must stay patient and respectful. — Robert McCoppin, Chicago Tribune, 5 Nov. 2026

Word History

Etymology

borrowed from Latin dēmentia "derangement, insanity, folly," noun derivative of Latin dēment-, dēmens "out of one's mind, frenzied, insane," from dē- de- + -ment, -mens, adjective derivative of ment-, mens "power of reason, mental balance, mind" — more at mind entry 1

First Known Use

1806, in the meaning defined at sense 1

Phrases Containing dementia

• dementia praecox
• dementia pugilistica
• senile dementia

Rhymes for dementia

• sententiae

Kids Definition

dementia

noun

de·​men·​tia di-ˈmen-chə 

1

: a condition of the brain that is marked especially by a deterioration in the ability to think, reason, or remember

2

: a condition of deteriorating mental functioning

Medical Definition

dementia

noun

de·​men·​tia di-ˈmen-chə 

: a usually progressive condition (as Alzheimer's disease) marked by the development of multiple cognitive deficits (as memory impairment, aphasia, and inability to plan and initiate complex behavior)

demential

-chəl 

adjective