This word for today is something I put up with a lot as a kid when I shared a room with my sister because she had a horrific habit of this and still does. It’s called Bruxism.
Bruxism is the involuntary grinding of teeth, especially while asleep.
Believe me, this one can be super annoying when it’s done loudly each night. My sister now, as an adult, uses a mouthpiece but chews through one about every six months. Wow, that’s a lot of grinding.
The word itself comes from the Greek word brukhein meaning “gnashing of teeth.”