mental deterioration of organic or functional origin
"The patient's memory loss and confusion indicated a progressive dementia caused by organic brain damage rather than simple forgetfulness."
A progressive decline in cognitive function due to damage or disease in the brain beyond what might be expected from normal aging. Areas particularly affected include memory, attention, judgement, language and problem solving.
"After his diagnosis of dementia, Arthur found that everyday tasks like managing finances or remembering where he had placed his keys became increasingly difficult due to the progressive damage in his brain."
In plain English: Dementia is a condition that causes serious memory loss and confusion, making it hard for someone to think clearly or take care of themselves.
"His memory loss was so severe that his family suspected he had dementia."
Usage: Avoid using "dementia" as a synonym for Alzheimer's disease, since it describes a broader category of conditions that includes but is not limited to Alzheimer's. Do not use the term casually to describe temporary forgetfulness or confusion caused by stress or fatigue.
The word dementia comes directly from Latin, where it originally described a state of foolishness or madness. It entered English with the same meaning to denote severe mental decline.