An Etymological Dictionary of the German Language/Annotated/brummen
brummen, verb, ‘to growl, snarl, grumble,’ from Middle High German brummen, weak verb, ‘to growl, hum,’ a deriv, of the Middle High German strong verb brimmen, ‘to growl, roar’ (compare the equivalent Middle English brimmen). This again is cognate with Middle High German brëmen, Old High German brëman, strong verb, ‘to growl, roar,’ since mm belongs properly only to the present and not to the other tenses. The cognates of the stem brëm-, which these verbs indicate, also includes Old Icelandic brim, ‘surge,’ Middle English brim, ‘glow’ (English brimstone); other related words may be found under Bremse. The Teutonic root brem, pre-Teutonic bhrëm, appears in Latin fremere, ‘to gnash,’ with which some are fond of comparing Greek βρέμεω, ‘to rumble.’ The Old Indian bhram as a verbal stem significs ‘to move unsteadily’; bhramá, neuter, ‘whirling flame,’ bhrmí, masculine, ‘whirlwind.’ Hence the meaning ‘to rush, gnash, crackle,’ seems to have been developed from a vibrating motion, especially that of sound. See the following word.