Meaning of EITHER in English
adj., pron., adv., & conj.
adj. & pron. 1 one or the other of two (either of you can go; you may have either book). 2 each of two (houses on either side of the road; either will do).
adv. & conj. 1 as one possibility (is either black or white). 2 as one choice or alternative; which way you will (either come in or go out). 3 (with neg. or interrog.) a any more than the other (I didn't like it either; if you do not go, I shall not either). b moreover (there is no time to lose, either). either-or n. an unavoidable choice between alternatives.
adj. involving such a choice. either way in either case or event.
[ OE gther f. Gmc ]
Concise Oxford English dictionary. Краткий оксфордский словарь английского языка. 2012