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
Recent Examples on the Web
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.
When Lancy's husband died after a struggle with dementia, she was exhausted. — Sam Gringlas, NPR, 27 Aug. 2026 Two years later, another study found that dementia care often misses or overlooks unique perspectives and needs of Latinos. — Hillary Lum, The Conversation, 27 Aug. 2026 If a woman’s brain fog is recorded as early signs of dementia, her anxiety as psychiatric condition, or her sleeplessness as an isolated complaint, the symptom or misdiagnosis may enter the medical record, but its connection to menopause disappears. — Yulin Hswen, STAT, 27 Aug. 2026 The project – selected for the Nordic Co-Production Market – sees an American dropout who tries to save her grandmother from dementia and accidentally triggers a zombie outbreak at a Norwegian nursing home. — Marta Balaga, Variety, 27 Aug. 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 1 Sep. 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

Last Updated: - Updated example sentences
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