"Gnash" is a verb that means to grind or clash your teeth together, usually in anger or frustration. It can also mean to make a harsh, grinding noise.

For example, if someone is really angry about something, they might gnash their teeth together in frustration. Or if two pieces of metal are rubbing together and making a loud, grating noise, you could say that they are gnashing against each other.

So, "gnash" means to grind or clash your teeth, or to make a harsh, grinding noise. It's like a forceful way of making a noise or showing your feelings!