One of two; the one or the other; properly used of two things, but sometimes of a larger number, for any one
You use either by itself in negative statements to indicate that there is a similarity or connection with a person or thing that you have just mentioned. He did not even say anything to her, and she did not speak to him either
after a negative statement used as an intensive meaning something like `likewise' or `also'; "he isn't stupid, but he isn't exactly a genius either"; "I don't know either"; "if you don't order dessert I won't either"
You use either in a negative statement in front of the first of two alternatives to indicate that the negative statement refers to both the alternatives. There had been no indication of either breathlessness or any loss of mental faculties right until his death
You use either in a negative statement to refer to each of two things, people, or situations to indicate that the negative statement includes both of them. She warned me that I'd never marry or have children. --- `I don't want either.' Either is also a quantifier. There are no simple answers to either of those questions. Either is also a determiner. He sometimes couldn't remember either man's name