Rictus is a noun that refers to a gaping mouth.

Our word of the day comes directly from Latin where it is translated into ‘open mouth.’ A person’s rictus refers to their mouth made wide open, usually in disgust or horror.

I didn’t know what had happened before I entered the room, but I could tell by Leslie’s rictus that something horrific had taken place. The grimace on her face made me shiver.