[ei.ther] adj [ME, fr. OE aeghwaether both, each, fr. a always + ge-, collective prefix + hwaether which of two, whether--more at aye, co-] (bef. 12c) 1: being the one and the other of two: each "flowers blooming on ~ side of the walk"
2: being the one or the other of two "take ~ road"
[2]either pron (bef. 12c): the one or the other [3]either conj (bef. 12c)--used as a function word before two or more coordinate words, phrases, or clauses joined usu. by or to indicate that what immediately follows is the first of two or more alternatives [4]either adv (15c) 1: likewise, moreover--used for emphasis after a negative "not smart or handsome ~"
2: for that matter--used for emphasis after an alternative following a question or conditional clause esp. where negation is implied "who answers for the Irish parliament? or army ~? --Robert Browning"