Strong’s Greek
G1031 — brucho
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
βρύχω
brucho — pronounced broo'-kho
a primary verb; to grate the teeth (in pain or rage):--gnash.
1 occurrence in the KJV.
Acts 7:54
When they heard these things, they were cut to the heart, and they gnashed on him with their teeth.