To grind your teeth together, usually in anger or pain.
From Old Norse 'gnastan' meaning to gnash or creak. Related to Old High German 'knirren.' The word likely imitates the grinding sound teeth make.
Gnash appears throughout literature and film as the ultimate sign of rage or anguish—it's the physical sound that anger makes! Animals also gnash their teeth when stressed, so it's a universal stress response across species.
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