/ ˈsiːnaɪl; NAmE / adjective
behaving in a confused or strange way, and unable to remember things, because you are old :
I think she's going senile .
► sen·il·ity / səˈnɪləti; NAmE / noun [ U ]:
an old man on the verge of senility
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WORD ORIGIN
mid 17th cent.: from French sénile or Latin senilis , from senex old man.