Either Definition

ēthər, īthər

pronoun

One or the other (of two)

Webster's New World

Francis Bacon (1561-1626)

Scarce a palm of ground could be gotten by either of the three.

Wiktionary

1590, Edmund Spenser, The Faerie Queene, III.i.

And either vowd with all their power and wit, / To let not others honour be defaste […]

Wiktionary

Oliver Wendell Holmes, Sr. (1809-1894)

There have been three talkers in Great British, either of whom would illustrate what I say about dogmatists.

Wiktionary

Synonyms:

Synonyms:
either-or
one
one of two
one or the other
as soon one as the other
each of two
this-one

conjuntion

The first element of the pair of disjunctive correlatives either … or, implying a choice of alternatives [either go or stay]

Bring either cookies, doughnuts, or some other kind of pastry.

Webster's New World

Used before the first of two or more coordinates or clauses linked by or:

Either we go now or we remain here forever.

American Heritage

adjective

One or the other (of two)

Use either hand.

Webster's New World

Each (of two); the one and the other.

He had a tool in either hand.

Webster's New World

adverb

Likewise; also. Used as an intensive following negative statements.

If you don't order a dessert, I won't either.

American Heritage

Any more than the other; also.

If you don't go, I won't either.

Webster's New World

Certainly; indeed.

“It's mine.” “It isn't either!”

Webster's New World

(conjunctive, after a negative) As well.

I don't like him and I don't like her either.

Wiktionary

determiner

Each of two. [from 9th c.]

Wiktionary

One or the other of two. [from 14th c.]

Wiktionary

(coordinating) Used before two or more not necessarily exclusive possibilities separated by "or" or sometimes by a comma.

You'll either be early, late, or on time.

Wiktionary

Origin of Either

Old English ǣġhwæþer, from Proto-Germanic, ultimately corresponding to ay + whether. Akin to Old Saxon eogihwethar, iahwethar; Old Dutch *iogewether, *iowether, *iother (Dutch ieder); Old High German eogihwedar, iegihweder, ieweder (German jeder).

From Wiktionary
Middle English from Old English ǣther, ǣghwæther kwo- in Indo-European roots

From American Heritage Dictionary of the English Language, 5th Edition