v. Simple past tense and past participle of dement.
the GNU version of the Collaborative International Dictionary of English
adj. Insane; mad; of unsound mind.
The Century Dictionary and Cyclopedia
Having lost the normal use of the reason; insane; specifically, afflicted with or characterized by dementia.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adj. affected with madness or insanity
Word Usage
"The word 'demented' like 'nutter' or 'lunatic' is a real barrier to sufferers, such as myself, in discussing mental illness, and so overcoming the terrible awkwardness that makes us feel like social lepers."