dementia
US
UK dementia n: (deterioration of mental faculties)
SC 痴呆 chī dāi
After Wayne became increasingly forgetful, he was diagnosed with dementia.
senile dementia n: (mental deterioration in old age)
SC 老年性痴呆 lǎo nián xìng chī dāi
As the years have passed, my grandfather's senile dementia has gotten worse.