Strong's Greek #5149 - τρίζω trizó (to cry)

gnash.

Apparently a primary verb; to creak (squeak), i.e. (by analogy) to grate the teeth (in frenzy) -- gnash.

Strong's 5149: τρίζω

τρίζω; to squeak, make a shrill cry (Homer, Herodotus, Aristotle, Plutarch, Lucian, others): transitive, τούς δωντας, to grind or gnash the teeth, Mark 9:18; κατά τίνος, Ev. Nicod. c. 5.

Strong's Greek: 5149. τρίζω (trizó) — 1 Occurrence

Mark 9:18 - V-PIA-3S
GRK: ἀφρίζει καὶ τρίζει τοὺς ὀδόντας
NAS: him [to the ground] and he foams [at the mouth], and grinds his teeth
KJV: and gnasheth with his
INT: he foams and gnashes his teeth