An Etymological Dictionary of the German Language/Annotated/Euter
Euter, masculine and neuter, ‘udder, dug,’ from the equivalent Middle High German iuter, ûter, Old High German ûtar, ûtiro, masculine; a word common to Teutonic and originally a primitively Aryan word, which has the same sense everywhere. Compare Dutch uijer, Anglo-Saxon ûder, English udder; also with gradation eudar in Middle Low German jeder, Old Frisian iader, Old Icelandic júgr. The-resulting Teutonic ûdr-, eudr-, from Aryan ûdhr-, corresponds to the equivalent Sanscrit ûdhar, Greek οὔθαρ (with gradation), Latin ûber; Slavonic vymę (from *vyd-men-), ‘udder,’ is differently derived.