dementia

noun

de·​men·​tia di-ˈmen(t)-shə How to pronounce dementia (audio)
-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 adjective

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.
The 47-year-old British-American model and author has assumed the rule of caretaker of her husband, Bruce Willis, amid his ongoing fight against frontotemporal dementia. Ryan Coleman September 2, EW.com, 3 Sep. 2025 Numerous studies have shown that while the number of people with dementia is increasing as the population ages, the proportion of older adults who develop dementia has been falling in the United States and several European countries. Paul Spann, Miami Herald, 3 Sep. 2025 One systematic review and meta-analysis published in 2023 found that older adults both with and without dementia experienced worsening cognitive functioning during social isolation. Casey Gueren, SELF, 3 Sep. 2025 The Lancet’s Commission on Dementia Prevention ranks hearing loss as the single most significant modifiable risk factor for developing dementia. Joseph Coughlin, Forbes.com, 2 Sep. 2025 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

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Cite this Entry

“Dementia.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/dementia. Accessed 10 Sep. 2025.

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 adjective

More from Merriam-Webster on dementia

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