senile

Etymology

1660s; borrowed from French sénile, from Middle French senile, from Old French senile, from Latin senīlis (“of or pertaining to old age”), from senex (“old man”), ultimately from Proto-Indo-European *sénos (“old”).

adj

1. Of, or relating to old age.
   Similar studies of rats have employed four different intracranial resorbable, slow sustained release systems— […]. Such a slow-release device containing angiogenic factors could be placed on the pia mater covering the cerebral cortex and tested in persons with senile dementia in long term studies. 2013 May-June, Charles T. Ambrose, “Alzheimer’s Disease”, in American Scientist, volume 101, number 3, page 200
2. (often offensive) Exhibiting the deterioration in mind and body often accompanying old age; doddering.
   Her mother was senile, but they called it dementia now. 2019, Colson Whitehead, The Nickel Boys, Fleet, page 183

noun

1. (dated, medicine) A person who is senile.
   Seniles differ markedly in their early adult intelligence level, and in their social, vocational, and educational histories. 1979, Oscar J. Kaplan, Psychopathology of Aging, page 54