/see"nuyl, -nil, sen"uyl/ , adj.
1. showing a decline or deterioration of physical strength or mental functioning, esp. 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 Geog. (of topographical features) having been reduced by erosion to a featureless plain that stands everywhere at base level. Cf. peneplain .
n.
4. a senile person.
[ 1655-65; senilis old, equiv. to sen ( ex ) old man (akin to SENIOR) + -ilis -ILE ]