Meaning of EITHER in English

EITHER

/ ˈaɪðə(r); NAmE ; ˈiːðə(r)/ determiner , pronoun , adverb

■ determiner , pronoun

1.

one or the other of two; it does not matter which :

You can park on either side of the street.

You can keep one of the photos. Either of them—whichever you like.

There are two types of qualification—either is acceptable.

➡ note at neither

2.

each of two :

The offices on either side were empty.

There's a door at either end of the corridor.

■ adverb

1.

used after negative phrases to state that a feeling or situation is similar to one already mentioned :

Pete can't go and I can't either.

( NAmE , informal )

'I don't like it.' 'Me either.' (= Neither do I) .

2.

used to add extra information to a statement :

I know a good Italian restaurant. It's not far from here, either.

3.

either ... or ... used to show a choice of two things :

Well, I think she's either Russian or Polish.

I'm going to buy either a camera or a DVD player with the money.

Either he could not come or he did not want to.

—compare or ➡ note at neither

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WORD ORIGIN

Old English ǣgther , contracted form of ǣg(e)hwæther , of Germanic origin; ultimately related to aye and whether .

Oxford Advanced Learner's English Dictionary.      Оксфордский английский словарь для изучающик язык на продвинутом уровне.