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.)
He has torn me in his wrath, and persecuted me. He has gnashed on me with his teeth. My adversary sharpens his eyes on me.
The wicked will see it, and be grieved. He shall gnash with his teeth, and melt away. The desire of the wicked will perish.
All your enemies have opened wide their mouth against you. They hiss and gnash the teeth; they say, "We have swallowed her up. Certainly this is the day that we looked for; we have found, we have seen it."
and wherever it seizes him, it throws him down, and he foams at the mouth, and grinds his teeth, and wastes away. I asked your disciples to cast it out, and they weren't able."
Now when they heard these things, they were cut to the heart, and they gnashed at him with their teeth.