An Etymological Dictionary of the German Language/Annotated/Bruder
Bruder, masculine, ‘brother, friar,’ from the equivalent Middle High German bruoder, Old High German bruodar; compare Gothic brôþar, Anglo-Saxon brôþor, English brother, Dutch broeder, Old Saxon brôthar. Inherited, like most words denoting kinship, from the period when all the Aryans formed only one tribe, without any difference of dialect; the degrees of relationship (compare Oheim, Vetter, Vase) at that period, which is separated by more than three thousand years from our era, were very fully developed. The primitive form of the word Bruder was bhrãtô(r), nominative plural bkrâtores; this is attested, according to the usual laws of sound, both by Gothic-Teutonic brôþar and Latin frâter, Greek φράτηρ, Old Indian bhrâtar-, Old Slovenian bratrŭ; all these worlds retain the old primary meaning, but in Greek the word has assumed a political signification.