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

That is the dementia of a filmmaker, where the movie comes first. — Marlow Stern, Variety, 21 Aug. 2026

Black people are two times more likely to develop dementia, according to the Alzheimer’s Association. — Justin Klawans, TheWeek, 21 Aug. 2026

Numerous renowned and highly respected psychiatrists have provided evidence that the president does show signs of dementia, in conjunction with unmistakable traits consistent with malignant narcissism and antisocial personality disorder. — Voice Of The People, New York Daily News, 20 Aug. 2026

With Bera’s office, Uribe also assisted in the congressman’s annual Brain Health Forum for people with dementia and their families. — Emma Hall, Sacbee.com, 20 Aug. 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