de·men·tia (d?-m?n?sh?)n. Loss of cognitive abilities, including memory, concentration, communication, planning, and abstract thinking, resulting from brain injury or from a disease such as Alzheimer’s disease or Parkinson’s disease. It is sometimes accompanied by emotional disturbance and personality changes.[Latin d?mentia, madness, from d?m?ns, d?ment-, senseless; see dement.]de·men?tial adj.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.dementia (d??m?n??; -???) n (Pathology) a state of serious emotional and mental deterioration, of organic or functional origin[C19: from Latin: madness; see dement]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014de?men?tia (d??m?n ??, -?i ?) n. severely impaired memory and reasoning ability, usu. with disturbed behavior, associated with damaged brain tissue. [1800?10;