Webster's Revised Unabridged Dictionary · 1913

Either

Either (ē"tẽr or ī"tẽr; 277) , adjective and pronoun

[Old English either, aither, Anglo-Saxon ageer, aghwaeer (akin to Old High German ēogiwedar, Middle High German iegeweder); ā + ge + hwaeer whether. See Each, and Whether, and compare Or, conj.]

1.
One of two; the one or the other; -- properly used of two things, but sometimes of a larger number, for any one.
Lepidus flatters both, Of both is flattered; but he neither loves, Nor either cares for him. — Shakespeare
Scarce a palm of ground could be gotten by either of the three. — Bacon
There have been three talkers in Great British, either of whom would illustrate what I say about dogmatists. — Holmes
2.
Each of two; the one and the other; both; -- formerly, also, each of any number.
His flowing hair In curls on either cheek played. — Milton
On either side... was there the tree of life. — Rev. xxii. 2
The extreme right and left of either army never engaged. — Jowett (Thucyd)

Either , conjunction

Either precedes two, or more, coordinate words or phrases, and is introductory to an alternative. It is correlative to or.
Either he is talking, or he is pursuing, or he is in a journey, or peradventure he sleepeth. — 1 Kings xviii. 27
Few writers hesitate to use either in what is called a triple alternative; such as, We must either stay where we are, proceed, or recede. — Latham
Can the fig tree, my brethren, bear olive berries? either a vine, figs? — James iii. 12

Either was formerly sometimes used without any correlation, and where we should now use or.