Pronunciation
Either has two different pronunciations in modern English. The pronunciation "ee-ther" /ˈiːðə(ɹ)/ (IPA) is usually encountered in American English, and is the pronunciation of the majority of English speakers. The pronunciation "eye-ther" /ˈaɪðə(ɹ)/ is associated with British English and Canadian English, but it is not universal in either place or 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 Great Britain; the king was a German who did not speak English as a native language, and was misled by English spelling. The new royal pronunciation was imitated by his courtiers, and as such became a new form. It is not likely that this is the source of the eye-ther pronunciation - before English spelling was fixed, it tended to be phonetic; as early as the 13th century, there are examples of the first vowels being spelled "ai", which would correspond to eye-ther.
An Ira Gershwin song, Let's Call the Whole Thing Off, opens with the words "You say ee-ther and I say eye-ther", and concerns a couple who lament the strain put on their relationship by pronunciation differences (and the different social backgrounds which they imply). In the end, happily, love conquers phonetics.
The 'ee-ther' pronunciation forms, with the word 'ether' one of the few minimal pairs demonstrating that the difference between the voiced dental fricative and the unvoiced dental fricative is phonemic in English.