de·ment·ed dəˈmen(t)əd/ adjective suffering from dementia. informal driven to behave irrationally due to anger, distress, or excitement. "a demented, dangerous, and sadistic Mafioso" synonyms: mad, insane, deranged, psychotic, out of one's mind, crazed, lunatic, unbalanced, unhinged, disturbed, non compos mentis;All Rights Reserved