An Etymological Dictionary of the German Language/Annotated/grunzen

by Friedrich Kluge

grunzen, verb, ‘to grunt,’ from the equivalent Middle High German and Old High German grunzen (Old High German *grunnazzen); corresponding to English to grunt (Middle English grunten); intensive form of Middle High German grinnen, Anglo-Saxon grunnian, ‘to gnash.’ The stem upon which it is based is probably imitative, as the similarly sounding Latin grunnire, Greek γρύζειν, lead us to suppose.