Hebrews harak, meaning "to grate the teeth", (Job 16:9; Psalm 112:10; Lamentations 2:16), denotes rage or sorrow. (See also Acts 7:54; Mark 9:18.)

Noah Webster's New International Dictionary of the English Language

1. (v. t.) To strike or grind together in anger; as, to gnash the teeth.

2. (v. i.) To grind or strike the teeth together.