either
UK: ˈaɪðə(r) | US: ˈiːðər
adj. one or the other of two
pron. one or the other of two people or things
conj. used before the first of two alternatives to indicate that they are each equally possible
The word "either" originates from Old English ǣgther, a contraction of ǣg (meaning "ever" or "always") and hwæther (meaning "which of two"). Over time, it simplified to "either," retaining its core function of presenting a binary choice. The morpheme ei- reflects the idea of "always" or "any," while -ther ties it to the concept of "the other," emphasizing duality.
You can choose either the red or the blue shirt.
Either of these options will work for the project.
She didn’t agree with either proposal.
Either we leave now, or we miss the train.
I haven’t been to either of those restaurants.