An Etymological Dictionary of the German Language/entweder

by Friedrich Kluge

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