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

All had extremely low omega-3 levels and at least one risk factor for dementia, such as obesity, sedentary lifestyle, high blood pressure or cholesterol. —Sandee Lamotte, CNN Money, 18 June 2026

Emma has taken on a caregiver role for Bruce in the last four years after he was diagnosed with aphasia and stepped away from acting in 2022 and received a frontotemporal dementia (FTD) diagnosis the following year. —Tommy McArdle, PEOPLE, 18 June 2026

For the study, published June 9 in the journal Nature Metabolism, the team analyzed University of Florida Health system records of more than 24,000 patients with dementia, including Alzheimer's, and almost 42,000 patients with mild cognitive impairment between 2012 and 2024. —Cathy Nelson, Health, 18 June 2026

In 2023, Bruce Willis was diagnosed with frontotemporal dementia, and since then, Heming Willis has taken on the role of his caregiver. —Felicity Abbott, CBS News, 17 June 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