• (n.) Dementia; loss of mental powers. See Insanity.
De'men·cy noun [ Latin dementia , from demens mad. See Dement .] Dementia; loss of mental powers. See Insanity . 
demency 1. Significant loss of intellectual abilities; such as, memory capacity, severe enough to interfere with social or occupational functioning. 2. A rarely used term for dementia.