Either is an English pronoun, adjective, and conjunction, meaning one, or the other, of two. Its origin is from Old English æghweþer, which literally analyses as a compound word "any - whether."
Either-or means "one, or the other, but not both."
Either and or are occasionally misleading terms in the sometimes loose interface between English and logic. They can be used to mean a simple logical disjunction between two alternatives (either one, or the other, or both); but either . . . or frequently implies an exclusive disjunction between two incompatible alternatives.
Either has two different pronunciations in modern English. SAMPA /i:D=r\\'/ ("ee-ther") is the pronunciation usually encountered in American English, and is the pronunciation of the majority of English speakers. The pronunciation /aID=r\\'/ ("eye-ther") is associated with British English and Canadian English, but it is not universal in either place, nor in Australian English and other dialects that take their lead from British English.
A recurring urban legend says that the eye-ther pronunciation originated with King George I or another of the Hanoverian kings of England; the king was a German who did not speak English as a native language, and was misled by English spelling. The new-modelled royal pronunciation was imitated by his courtiers, and as such became a prestige form among those subject to their influence. At this remove, this tale is hard to confirm or disconfirm.
A frequent difficulty in English usage concerns the permissibility of using either to refer to more than one alternative. Generally, either refers to exactly two alternatives. When there are more, linguistic prescriptivists counsel the use of any. One generally accepted exception to this rule is when either is used as a conjunction to introduce a string of either . . . or alternatives:
Pronunciation
Usage
Any is not used as a conjunction, and cannot be used in this context.
