aether

Etymology
From.

Noun

 * 1) the upper, pure, bright air; ether; the heavens
 * 2) the air or sky; light of day
 * 3) the upper world, the earth (as opposed to the lower world)
 * 4) the brightness or ethereal matter surrounding a deity

Declension
Note that, in Late Latin, the plural is sometimes written as aethera. The genitive occasionally appears as the Ancient Greek, aetheros.