Webster’s Revised Unabridged Dictionary · 1913
Gnash
Gnash (năsh), v. t. [imp. & p. p. Gnashed (#); p. pr. & vb. n. Gnashing.] [OE. gnasten, gnaisten, cf. Icel. gnastan a gnashing, gnīsta to gnash, Dan. knaske, Sw. gnissla, D. knarsen, G. knirschen.] To strike together, as in anger or pain; as, to gnash the teeth.
Gnash, v. i. To grind or strike the teeth together.
There they him laid, Gnashing for anguish, and despite, and shame. Milton.