dementia

noun

de·​men·​tia di-ˈmen(t)-shə How to pronounce dementia (audio)
-shē-ə
Synonyms of dementianext
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 How to pronounce dementia (audio)
-shē-əl
adjective

Synonyms of dementia

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Examples of dementia in a Sentence

This patient suffers from dementia. a new study on age-related dementias
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Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Other symptoms include mild dementia that involves short-term memory loss, a lack of interest in daily activities and difficulty completing routine tasks. — Andrea Flores, Los Angeles Times, 16 Oct. 2026 That’s because perimenopause is around the time when brain changes start occurring that could lead towards dementia, like build-up of proteins like taus and amyloids in the brain. — Maggie Ryan, Flow Space, 14 Oct. 2026 As a final demonstration of this approach’s promise, the researchers designed zinc proteases that could target proteins associated with neurological disorders, such as Alzheimer’s and frontotemporal dementia. — ArsTechnica, 14 Oct. 2026 But in diseases known as tauopathies, including Alzheimer’s disease and frontotemporal dementia, tau can misfold. — Mike McRae 13, New Atlas, 14 Oct. 2026 See All Example Sentences for dementia

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

Time Traveler
The first known use of dementia was in 1806

Phrases Containing dementia

Rhymes for dementia

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Browse Nearby Words

démenti
dementia
demential
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Cite this Entry

“Dementia.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/dementia. Accessed 19 Oct. 2026.

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Kids Definition

dementia

noun
de·​men·​tia di-ˈmen-chə How to pronounce dementia (audio)
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 How to pronounce dementia (audio)
: 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 How to pronounce dementia (audio)
adjective

More from Merriam-Webster on dementia

Britannica.com: Encyclopedia article about dementia

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