Gnash (verb)

1. To grind (the teeth) together, typically as an expression of anger, frustration, or pain.
2. To make a harsh grinding noise.

Origin:

Middle english gnashen, from old english gnæscan, from gnæscan to bite.

Examples:

1. The prisoner gnashed his teeth in frustration.
2. The horse gnashed its teeth and neighed in fear.
3. She gnashed her teeth in anger at her opponent's move.
4. The gears of the old car gnashed as the driver shifted into reverse.
5. The wind gnashed through the trees, making a loud howling noise.