aether

Definitiones

1. sky, ether (distinct in this sense from caelum (“heaven”), which is where the night's stars are, but not always distinguished from āēr; always distinct from the underworld)
   declension-3
2. the substance filling the sky above the clouds (above the tropopause), distinct from āēr at cloud level and below
   Greek, declension-3
3. ether, quintessence
   Medieval-Latin, New-Latin, declension-3

Aequivalentia

Gradus CEFR