Definition of either :
1. Each of two; the one and the other; both; - formerly, also, each of any number.
2. One of two; the one or the other; - properly used of two things, but sometimes of a larger number, for any one.
3. precedes two, or more, coordinate words or phrases, and is introductory to an alternative. It is correlative to or.
too, not...anything better/worse, additionally, in any case, incidentally, every, of your life, namely, yet, moreover, also, with/without distinction, anyway, whether or not, furthermore, again, it could be that, withal, then, all, even so, any, besides, by the way, ultimate, one or the other, each, not to mention, further, unadulterated, couldn't be better/worse/nicer etc., like nothing on earth, unbelievable, the fact that, anyhow, likewise, it might be that, conspicuous, there's nothing better, worse, more exciting etc. than, unless
dual (part of speech: adjective)