Either, a. & pron.
Etymology: [OE. either, aither, AS. , (akin to OHG. , MHG. iegeweder); a + ge + hwæ whether. See Each, and Whether, and cf. 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. Shak. 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).
1 other Webster entry under this spelling
Either, conj. Either
precedes two, or more, coördinate 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.
Note: Either was formerly sometimes used without any correlation, and where we should now use or. Can the fig tree, my brethren, bear olive berries either a vine, figs James iii. 12.
Shades of meaning
Fernald has no entry of its own for either; he lists it under every.
Where he writes about it:
Either properly denotes one of two, indefinitely, to the exclusion of the other. — from every
The use of either in the sense of each or both, tho sustained by good authority, is objectionable because ambiguous. — from every
His friends sat on either side of the room would naturally mean on one side or the other; if the meaning is on both sides, it would be better to say so. — from every