To gnash your teeth means to grind them together forcefully, usually because you're angry, frustrated, or in pain. When someone gnashes their teeth, you can often hear a scraping, grinding sound as their top and bottom teeth rub against each other.

People gnash their teeth when they're so upset they can barely contain themselves. A soccer player who just missed an easy goal might gnash his teeth in frustration. Someone experiencing terrible pain might gnash their teeth while trying to endure it. The word captures that physical expression of intense emotion, when feelings become so strong they show up in your body.

You'll often see this word in stories and poems to show extreme anger or suffering. A villain might “gnash his teeth” in rage when the hero escapes. In older literature, people sometimes describe punishment as a place of “weeping and gnashing of teeth,” emphasizing both sorrow and anguish.

Most people don't literally gnash their teeth very often in real life, but the word gives writers a vivid way to show someone experiencing powerful, overwhelming emotions.