Eevee’s planned English name before its final rename was Eon.
Eevee was first introduced in Pokémon Red and Blue as a Normal-type Pokémon capable of branching into multiple forms. Before the English-language games were released, the localization team considered calling the Pokémon “Eon,” a name connected to its evolutionary theme and the word “eon.”
The final English name, Eevee, was chosen before the international releases. It resembles the Japanese name Eievui and also echoes the letter sound used in the names of its first three evolutions: Vaporeon, Jolteon, and Flareon.
Eevee’s naming history is easy to confuse with the later fan term “Eeveelution,” which describes its evolved forms. “Eon” was an unused planned name for Eevee itself, not the name of a specific evolution or an official alternate species.