Either/ˈiːðər,ˈaɪðər/ Definition 1 of 4Pro Tip 1/3Choice Implication Implies exclusivity between choices; selecting one option means not selecting the other. You must either study law or medicine. Pro Tip 2/3Equal Probability Suggests both options are equally likely or possible, doesn't favor one over the other. It might either rain or snow tomorrow. Pro Tip 3/3Mutual Exclusivity Used when the two possibilities cannot both occur at the same time. The door must be either closed or open, not both.