Origin: 1535–45; < Late Latindēmentāre to deprive of mind, equivalent to Latindēment- (stem of dēmēns) out of one's mind (dē-de- + ment- (stem of mēns) mind) + -āre infinitive suffix
1540s, "to drive mad," probably from M.Fr. dementer, from L.L. dementare "out of one's mind," from phrase de mente, from de + mente, ablative of mens mind" (see mind (n.)).