An Etymological Dictionary of the German Language/Annotated/knirschen

knirschen, verb, ‘to gnash,’ Middle High German *knirsen, may be inferred from knirsunge, feminine, ‘gnashing,’ and zerknürsen, ‘to crush, squash’; for sch from s after r compare Hirsch and Arsch; compare Modern Dutch knarsen, knersen, ‘to gnash, crash,’ knarsetanden, ‘to gnash with the teeth.’