de·men·tia 
/dɪˈmɛnʃə/ noun
plural de·men·tias /dɪˈmɛnʃə/ noun medical : a mental illness that causes someone to be unable to think clearly or to understand what is real and what is not real [noncount] ▪ This patient suffers from dementia. [count] ▪ a new study on age-related dementias — see also senile dementia
