either

determiner: one or the other of two choices (used before a noun)
- Choose either option to continue.
determiner: each of two (used with a singular noun to refer to both separately)
- There were guards on either side of the door.
conjunction: used with ‘or’ to introduce alternatives
- Either we leave now or we’ll miss the train.
adverb: also; too (used after a negative statement)
- I don’t like this plan either.