Is dementia a terminal disease?

My Nana lives with us and was just diagnosed with dementia today. She is so forgetful and she's getting harder to care for because she refuses to do stuff on her own. Like I need to help her shower and comb her hair. She can't figure out how to make a sandwich even. It's like looking after a whole other child. I love her, but I can't do it anymore.

So much happened today but one of the things that stood out was the doctor saying that dementia is a terminal illness and I can't find anything to support that online. I see it's life limiting and eventually they'll die from it but when I think terminal I think cancer! Did he just say it wrong or ... Is it terminal because thetes just no cure? But then why isn't her diabetes a terminal illness?

Why is it called terminal? I'm just feeling a lot of things right now and it's just me and my husband. Everyone else is out of state and my parents have been on a missions trip for the last four months, which is why I have my grandma with me.