Quenya: Imperative of to be, literally let it be
The World, the Universe in Elven cosmology. The realisation of the Music of the Ainur which begun to exist when the Creator said "Eš", hence considered by Elves its name. It comprises Arda, the heavens and is animated by the SecretFire, bound by the priciples of space, time and matter. Outside Eš are the TimelessHalls and the Void.
Tolkien considered in a personal text the notion that other planets apart Arda (Earth) could exist in Eš but there would be no way for the EruhŪni to know about it.
|Therefore I say: Eš! Let these things Be! And I will send forth into the Void the Flame Imperishable, and it shall be at the heart of the World, and the World shall Be; and those of you that will may go down into it. And suddenly the Ainur saw afar off a light, as it were a cloud with a living heart of flame; and they knew that this was no vision only, but that Ilķvatar had made a new thing: Eš, the World that is.|
|The Silmarillion "Music of the Ainur"|