Psychiatry a disorder of the mind affecting perception, memory, and judgment, characterized by reduced ability to remember, control muscular movements, recognize familiar objects and sounds, etc.
L, insanity < demens: see dement
See dementia in American Heritage Dictionary 4
Deterioration of intellectual faculties, such as memory, concentration, and judgment, resulting from an organic disease or a disorder of the brain. It is sometimes accompanied by emotional disturbance and personality changes.