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

More than 7 in 10 older adults have more than one chronic condition, such as diabetes, cardiovascular disease, dementia or osteoporosis. — Minakshi Raj, The Conversation, 24 July 2026

And then there are long-term risks involving prolonged exposure to smoke and other air pollution, which has been linked to some cancers and dementia. — Seth Borenstein, Los Angeles Times, 22 July 2026

Those in the highest flavonoid-intake group were about 40% less likely to develop dementia than those in the lowest. — Samantha Agate, Fort Worth Star-Telegram, 22 July 2026

Just days before the doc’s 2024 release, Williams’ care team revealed that she had been diagnosed with primary progressive aphasia and frontotemporal dementia. — Charisma Madarang, Rolling Stone, 22 July 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