1. pronoun /ˈiːð.ə(ɹ),ˈaɪð.ə(ɹ)/
One or other of two people or things.
Than ayther departed to theire tentis and made hem redy to horsebacke as they thought beste.
2. adverb /ˈiːð.ə(ɹ),ˈaɪð.ə(ɹ)/
as well
I dont like him and I dont like her either.
3. conjunction /ˈiːð.ə(ɹ),ˈaɪð.ə(ɹ)/
Introduces the first of two options, the second of which is introduced by "or".
Either you eat your dinner or you go to your room.
Wikipedia foundation.