Either a. & pron. : One of two; the one or the other; -- properly used of two things, but sometimes of a larger number, for any one.

Either a. & pron. : Each of two; the one and the other; both; -- formerly, also, each of any number.

Either conj. Either : precedes two, or more, coordinate words or phrases, and is introductory to an alternative. It is correlative to or.

Example:
What is the main difference Either using the preterite vs imperfect?

Taxonomy
pronunciation, either/or, adjective, alternatives, English, conjunction, pronunciation differences, free encyclopedia, law, the eye, two choices, driveway, palm trees, price, pronoun, adverb, Logic, philosophy.

Defination from the web:
either and or is occasionally of import in law, such as in the interpretation of statutes and contracts. ... In philosophy, the first book Søren Kierkegaard published under a pseudonym was titled Either/Or (Danish: Enten/Eller) ...