Word Origin & History
demented
1644, from obsolete dement "drive mad" (1545), probably from M.Fr. dementer, from L.L. dementare "out of one's mind," from phrase de mente, from de + mente, abl. of mens mind." Dementia is attested from 1806; earlier form in Eng. was demency (1858), from Fr. démence. Dementia præcox is a Mod.L. form recorded from 1899 in Eng., 1891 in Ger., from Fr. démence précoce (1857). See precocious.