When a person has senility, old age has worn their mind down. They may forget names, lose the day of the week, wander, or say things that do not fit the room they are in. The word is a little old-fashioned. Doctors today more often say dementia, because senility quietly mixes “being old” with “being confused” — though actually many older people stay sharp, and the confused ones do not all have the same illness. In ordinary talk it can sound unkind, as if getting old must mean getting silly. It is a noun for the state. The person is senile; the state is senility.

衰老；（因年邁而）心智糊塗。現在較常、也較尊重地說「失智」，兩者不完全同一回事。