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

Emma Heming Willis is opening up about the ongoing grief her family experiences as her husband, Bruce Willis, lives with frontotemporal dementia. — Sameen Chaudhry, USA Today, 9 Sep. 2026

Entertainment Weekly has an exclusive look inside Emma Heming Willis’ life with Bruce Willis amid the Die Hard star’s dementia battle. — Joey Nolfi, Entertainment Weekly, 9 Sep. 2026

Since expanding from theater into film, writer-director Florian Zeller has specialized in examining the pressure of mental health issues on families — dealing with dementia in The Father and depression in The Son, both based on his plays. — David Rooney, HollywoodReporter, 8 Sep. 2026

During that time, almost 4,000 of the women were diagnosed with dementia—and those who’d used some form of MHT were about 10% less likely to be in that group, compared with women who hadn’t. — Jamie Ducharme, HEALTH, 8 Sep. 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