If you're looking for meanings of the word senility, please see a list of them below. Noun Infirmity due to extreme age. [Latin] Senile derangement; the vital exhaustion of Protozoa (biol.). Old agedness; dotage. the state of being senile Old age, especially as manifested by physical or mental weakness or decay. Senile derangement ; the vital exhaustion of Protozoa. Feebleness of body and mind incident to old age. Old age. The sum of the physical and mental changes occurring in advanced life. mental infirmity as a consequence of old age; sometimes shown by foolish infatuations Old age; dotage. Same as senilis, q. v.