An Etymological Dictionary of the German Language/grunzen

by Friedrich Kluge

grunzen, vb., ‘to grunt,’ from the equiv. MidHG. and OHG. grunzen (OHG. *grunnazzen); corresponding to E. to grunt (MidE. grunten); intensive form of MidHG. grinnen, AS. grunnian, ‘to gnash.’ The stem upon which it is based is probably imitative, as the similarly sounding Lat. grunnire, Gr. γρύζειν, lead us to suppose.