Origins
The word 'demented' entered English in the seventeenth century, either borrowed directly from Latin βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ'dΔmentΔtus' or formed in English from the verb 'dement' (now rare) plus the participial suffix '-ed.' The underlying Latin adjective is 'dΔmΔns' (genitive 'dΔmentis'), meaning 'out of one's mind' or 'insane,' composed of 'dΔ-' (away from, down from) and 'mΔns' (mind, intellect, reason). The PIE root is *men- (to think), one of the most fundamental cognitive roots in the language family.
The Latin noun 'mΔns' (mind) generated a vast family of English words. 'Mental' (pertaining to the mind), 'mentality' (a way of thinking), 'mention' (to bring to mind), 'mentor' (from the Greek proper name Mentor, who guided Odysseus's son Telemachus β the name itself from *men-, meaning 'one who thinks/advises'), 'memento' (a reminder, from Latin 'mementΕ,' remember β imperative of 'meminisse,' to remember), 'comment' (from Latin 'commentΔrΔ«,' to think over), 'reminisce' (to remember again), and 'dementia' (the state of being out of one's mind).
The PIE root *men- appeared in every branch of the family. In Greek: 'mΓ©nos' (spirit, force, mind), 'mnΔmΔ' (memory β source of 'mnemonic'), 'manΓa' (madness β source of 'mania,' 'maniac'), 'automatos' (self-thinking β source of 'automatic'). In Sanskrit: 'manas' (mind), 'mantra' (a thought-instrument, a sacred utterance β literally a 'thinking tool'). In the Germanic branch: Old English 'gemynd' (memory, mind β ancestor of modern 'mind'), 'munan' (to think, to remember), and 'minne' (memory, love β German 'Minne,' as in Minnesang, 'love-song').
Latin Roots
The medical term 'dementia' β now the standard clinical term for the progressive decline of cognitive function β was used by the Roman medical writer Celsus in the first century CE. It entered modern medical vocabulary in the eighteenth century when Philippe Pinel and others began classifying mental disorders systematically. The most common form, Alzheimer's disease (identified by Alois Alzheimer in 1906), accounts for approximately 60-70% of dementia cases.
The adjective 'demented' has both a clinical and an informal usage. Clinically, it describes a person suffering from dementia β experiencing progressive cognitive decline, memory loss, and impaired reasoning. Informally, it means 'wildly irrational' or 'crazy' β 'a demented plan,' 'a demented laugh.' The informal sense is much older than the clinical one and preserves the original Latin meaning more directly: a person driven out of their mind, not by disease but by passion, obsession, or external forces.
The prefix 'dΔ-' (away from, down from) appears in many English words describing loss or removal: 'depart' (to go away from), 'decline' (to lean away from), 'degrade' (to step down from), 'deprive' (to take away from). In 'demented,' it creates the image of a mind that has gone away β a person separated from their own faculty of reason. The word thus encodes not just the state of irrationality but the direction of its arrival: a moving away from sanity, a departure from the mind.