Etymology From Middle English gnasten. Origin unknown; the word is probably either Germanic or onomatopoeic. Compare Old Norse gnastan, Danish gnaske ("munch", "crunch"), German knirschen, German Low German gnirschen, gnörschen (“gnash”), Swedish gnissla (“squeak; gnash”).
There they were, boiling up in snowy spouts of spray, smiting and gnashing together like the gleaming teeth of hell.1886 October – 1887 January, H[enry] Rider Haggard, She: A History of Adventure, London: Longmans, Green, and Co., published 1887, →OCLC:
Etymology From Middle English gnasten. Origin unknown; the word is probably either Germanic or onomatopoeic. Compare Old Norse gnastan, Danish gnaske ("munch", "crunch"), German knirschen, German Low German gnirschen, gnörschen (“gnash”), Swedish gnissla (“squeak; gnash”).