Heb harak, meaning "to grate the teeth", (Job 16:9; Ps 112:10; La 2:16), denotes rage or sorrow. (See also Ac 7:54; Mr 9:18.)
And, wherever it seizes him, it dashes him down; he foams at the mouth and grinds his teeth, and he is pining away. I asked your disciples to drive the spirit out, but they failed."
As they listened to this, the Council grew frantic with rage, and gnashed their teeth at Stephen.