An Etymological Dictionary of the German Language/Annotated/entweder

by Friedrich Kluge

entweder, particle, ‘either,’ from Middle High German eintwëder, an uninflected neuter, corresponding as a disjunctive particle to an oder following; in Middle High German eintwëder, is mostly a pronoun (sometimes with oder following, ‘one of two,’ corresponding to Old High German ein-de-wëder (*ein-dih-wëdar), ‘one of two’; see weder. The origin of the Old High German de- is obscure; see kein.