Word Origin & History
either O.E. ægðer, contraction of æghwæðer "each of two, both," from a "always" + ge- collective prefix + hwæðer "which of two, whether." Modern sense of "one or the other of two" is early 14c. Use of either-or to suggest an unavoidable choice between alternatives (1931) in some cases reflects Dan. enten-eller, title of an 1843 book by Kierkegaard.
[url-http://www.dictionary.com/browse/either]In another place[/url], the following note is made:
Old English ǣgther, short for ǣghwæther each of two; related to Old Frisian ēider, Old High German ēogihweder; see each, whether