When you clench your teeth or they clench, you squeeze your teeth together firmly, usually because you are angry or upset. Patsy had to clench her jaw to suppress her anger Slowly, he released his breath through clenched teeth. = grit
When you clench your fist or your fist clenches, you curl your fingers up tightly, usually because you are very angry. Alex clenched her fists and gritted her teeth She pulled at his sleeve and he turned on her, fists clenching again before he saw who it was. angry protestors with clenched fists