either

[ee-th er, ahy-th er] /ˈi ðər, ˈaɪ ðər/

adjective

one or the other of two:

You may sit at either end of the table.

each of two; the one and the other:

There are trees on either side of the river.

pronoun

one or the other:

There are two roads into the town, and you can take either. Either will do.

conjunction

(a coordinating conjunction that, when preceding a word or statement followed by the disjunctive or, serves to emphasize the possibility of choice):

Either come or write.

adverb

also; too; as well; to the same degree (used after negative clauses coordinated by and, or, or nor, or after negative subordinate clauses):

He's not fond of parties, and I'm not either. If you don't come, she won't come either.

Origin

before 900; Middle English; Old English ǣgther, contraction of ǣghwæther each of two, both; see ay¹, whether

Can be confused

either, neither (see usage note at the current entry; see usage note at neither)

either, ether.

Usage note

When the pronoun either is the subject and comes immediately before the verb, the verb is singular: Either is good enough. Either grows well in this soil. When either is followed by a prepositional phrase with a plural object, there is a tendency to use a plural verb, but a singular verb is more common: Either of them is (or are) good enough. Either of the shrubs grows (or grow) well in this soil.
As an adjective either refers only to two of anything: either side of the river; using either hand. As a pronoun either sometimes occurs in reference to more than two ( either of the three children ), but any is more common in this construction ( any of the three children ). As a conjunction, either often introduces a series of more than two: The houses were finished with either cedar siding or stucco or brick. The pizza is topped with either anchovies, green peppers, or mushrooms.
Usage guides say that the verb used with subjects joined by the correlative conjunctions either … or (or neither … nor) is singular or plural depending on the number of the noun or pronoun nearer the verb: Either the parents or the school determines the program. Either the school or the parents determine the program. Practice in this matter varies, however, and often the presence of one plural, no matter what its position, results in a plural verb: Either the parents or the school determine the program.
In carefully edited writing, these correlative conjunctions are usually placed so that what follows the first correlative is parallel to what follows the second: The damage was done by either the wind or vandals or either by the wind or by vandals (not done either by the wind or vandals). See also neither.

Pronunciation note

The pronunciations

[ee-th er] /ˈi ðər/ (Show IPA) and

[nee-th er] /ˈni ðər/ with the vowel

[ee] /i/ of see, are the usual ones in American English for the words either and neither. The pronunciations

[ahy-th er] /ˈaɪ ðər/ and

[nahy-th er] /ˈnaɪ ðər/ with the

[ahy] /aɪ/ vowel of bite, occur occasionally for these words, chiefly in the speech of the educated and in the network standard English of radio and television. Both the

[ee] /i/ and

[ahy] /aɪ/ pronunciations existed in British English, and in the 19th century the

[ahy] /aɪ/ came to predominate in standard British speech. In American English, therefore, it reflects a recent borrowing from British speech rather than a survival from the time of early settlement, influenced as well by the ei spelling, which is pronounced as

[ahy] /aɪ/ in such words as height and stein.

Examples from the web for either

Without it, they either don't bloom, or flower poorly.
They can be made ahead, and they take well to either buffet or plated service.
And you probably didn't worry over a color wheel for hours when you decorated your house, either.
On the other hand, beans and wienies aren't exactly a cheery prospect, either.
either it's tasteless or it leaves you feeling empty.
Made of either translucent or opaque plastic, many have oversize openings with screw-on lids.
Note that heavy feeding of either type in spring leads to excessive leafy growth, soft fruit, and fruit rot.
Candle sconces on either side of the mirror add drama at night.
The room widens almost imperceptibly, then narrows again as the adobe walls converge on either side of the altar.
They also can be exceptionally convenient if you buy them peeled and deveined, either fresh or frozen.

British Dictionary definitions for either

either

/ˈaɪðə; ˈiːðə/

determiner

one or the other (of two): either coat will do
(as pronoun): either is acceptable

both one and the other: there were ladies at either end of the table

(coordinating) used preceding two or more possibilities joined by "or": you may have either cheese or a sweet

adverb (sentence modifier)

(used with a negative) used to indicate that the clause immediately preceding is a partial reiteration of a previous clause: John isn't a liar, but he isn't exactly honest either

Usage note

Either is followed by a singular verb in good usage: either is good; either of these books is useful. Care should be taken to avoid ambiguity when using either to mean both or each, as in the following sentence: a ship could be moored on either side of the channel. Agreement between the verb and its subject in either…or… constructions follows the pattern given for neither…nor…

Word Origin

Old English ǣgther, short for ǣghwæther each of two; related to Old Frisian ēider, Old High German ēogihweder; see each, whether

Word Origin and History for either

adj.

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.