senile

adjective

1. showing a decline or deterioration of physical strength or mental functioning, especially short-term memory and alertness, as a result of old age or disease.
2. of or belonging to old age or aged persons; gerontological; geriatric.
3. Physical Geography. (of topographical features) having been reduced by erosion to a featureless plain that stands everywhere at base level.Compare peneplain.

noun

4. a senile person.

adjective

1. of, relating to, or characteristic of old age
2. mentally or physically weak or infirm on account of old age
3. (of land forms or rivers) at an advanced stage in the cycle of erosionSee old (def. 18)

adj.1660s, “suited to old age,” from French sénile (16c.), from Latin senilis “of old age,” from senex (genitive senis) “old, old man,” from PIE root *sen- “old” (cf. Sanskrit sanah “old;” Avestan hana- “old;” Old Persian hanata- “old age, lapse of time;” Armenian hin “old;” Greek enos “old, of last year;” Lithuanian senas “old,” senis “an old man;” Gothic sineigs “old” (used only of persons), sinistra “elder, senior;” Old Norse sina “dry standing grass from the previous year;” Old Irish sen, Old Welsh hen “old”). Meaning “weak or infirm from age” is first attested 1848. adj.

1. Relating to, characteristic of, or resulting from old age.
2. Exhibiting the symptoms of senility, as impaired memory or the inability to perform certain mental tasks.