aether

|ˈēθər| |ˈiθər| |ˈiːθə|

noun

(aether) chiefly  poetic/literary  the clear sky; the upper regions of air beyond the clouds.

(aether) archaic Physics a very rarefied and highly elastic substance formerly believed to permeate all space, including the interstices between the particles of matter, and to be the medium whose vibrations constituted light and other electromagnetic radiation.

ORIGIN from Greek aithēr ‘upper air,’  from the base of aithein, ‘burn, shine.‘  Originally the word denoted a substance believed to occupy space beyond the sphere of the moon.