Definitions for eitherˈi ðər, ˈaɪ ðər; ˈi ðər; ˈni ðər; ˈaɪ ðər; ˈnaɪ ðər; aɪ

Random House Webster's College Dictionary

ei•ther^*ˈi ðər, ˈaɪ ðər; ˈi ðər; ˈni ðər; ˈaɪ ðər; ˈnaɪ ðər; aɪ(adj.)

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.
(pron.)one or the other:
Either will do.
Category: Function Word
(conj.)(a coordinating conjunction that, when used with or, indicates a choice):
Either call or write.
Category: Function Word
(adv.)as well; likewise (used after negative clauses):
If you don't go, I won't either.

^* Usage: When used as the subject, the pronoun either usually takes a singular verb even when followed by a prepositional phrase with a plural object: Either of the shrubs grows well in this soil. As an adjective either refers only to two of anything. As a pronoun either sometimes occurs in reference to more than two (either of the three children), but any is more common (any of the three children). As a conjunction, either often introduces a series of more than two: pizza topped with either onions, 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 varies, however, and often the presence of one plural, no matter where, results in a plural verb. See also neither.Pron: In American English, either and neither are usu. pronounced asandwith the vowel of see. The pronunciationsandwith the vowel of bite, occur chiefly among the educated and in the network standard English of radio and television. Both (ē) and (ī) pronunciations existed in 17th-century Britain, but it was not until the 19th century thatcame to predominate there. In American English,therefore reflects a recent borrowing rather than a survival from the time of early settlement.

Origin of either:

bef. 900; ME; OE ǣgther, contr. of ǣghwæther each of two, both; see ay , whether

Princeton's WordNet

either(adverb)
after a negative statement used as an intensive meaning something like `likewise' or `also'
"he isn't stupid, but he isn't exactly a genius either"; "I don't know either"; "if you don't order dessert I won't either"

Kernerman English Learner's Dictionary

either(pronoun)ˈi ðər, ˈaɪ ðər
one of two people or things
"Orange or apple juice?" "Either is fine"; Either of your parents can sign the form.
either(conjunction)ˈi ðər, ˈaɪ ðər
indicates that a choice is offered
Either send them to me, or I could come and get them.
either(adverb)ˈi ðər, ˈaɪ ðər
indicates another fact in a negative sentence
I don't like Chris, and I don't like his brother either.
either(determiner)ˈi ðər, ˈaɪ ðər
both things or people
Either player can start the game.

Wiktionary

either(Adverb)
as well
I don't like him and I don't like her either.
either(Pronoun)
Both, each of two (people or things).
either(Pronoun)
One or other of two people or things.
either(Conjunction)
Introduces the first of two options, the second of which is introduced by "or".
Either you eat your dinner or you go to your room.

Origin: æghwæþer, from West , ultimately corresponding to ay + whether

Webster Dictionary

Either(u)
one of two; the one or the other; -- properly used of two things, but sometimes of a larger number, for any one
Either(u)
each of two; the one and the other; both; -- formerly, also, each of any number
Either(u)
precedes two, or more, coordinate words or phrases, and is introductory to an alternative. It is correlative to or