nash (charaq; brugmos): "Gnash" is used of grinding or striking together the teeth in rage, pain or misery of disappointment. In the Old Testament it is the translation of charak, a mimetic word, and represents for the most part rage, anger, hatred (Job 16:9, "He gnasheth upon me with his teeth," the Revised Version (British and American) "hath gnashed upon me"; Ps 35:16; 37:12; 112:10, grief; La 2:16, contempt or derision); brucho, "to gnash the teeth in rage," indicates anger, rage, Septuagint for charaq (Ac 7:54, of Stephen, "They gnashed on him with their teeth"). The several instances of brugmos, "gnashing," in the Gospels seem to express disappointment rather than anger (Mt 8:12,"There shall be wailing and gnashing of teeth," the Revised Version (British and American) "the weeping and the gnashing of teeth"; Mt 13:42,50; 22:13; 24:51; 25:30; Lu 13:28--a vivid representation of the misery of disappointed expectations; compare Ecclesiasticus 30:10, "lest thou shalt gnash thy teeth in the end," gomphiazo, "to have the teeth set on edge"); trizo (Mr 9:18), which means "to give out a creaking, grating sound," "to screak," is used in the New Testament (in the above instance only) to mean "to grate or gnash with the teeth," indicating the effect of a paroxysm, the Revised Version (British and American) "grindeth his teeth."
⇒See the definition of gnash in the KJV Dictionary
W. L. Walker