either (adj.) Look up either at Dictionary.com
Old English ægðer, contraction of æghwæðer "each of two, both," from a "always" (see aye (adv.)) + ge- collective prefix + hwæðer "which of two, whether" (see whether).

Cognate with Dutch ieder, Old High German eogiwedar, German jeder "either, each, every"). Modern sense of "one or the other of two" is late 13c. Use of either-or to suggest an unavoidable choice between alternatives (1931) in some cases reflects Danish enten-eller, title of an 1843 book by Kierkegaard.