brightness, splendor (of heavenly bodies); clear/bright sky; heavens
Latin word, found 18 times in the texts on Socratos.
Vergil, Aeneid 3.585: Nam neque erant astrorum ignes, nec lucidus aethra
Ovid, Heroides 10.131: Nec pater est Aegeus, nec tu Pittheidos Aethrae
Lucretius, De Rerum Natura 6.467: vertice de montis videantur surgere in aethram.
All forms of aethra