etherion

== English == === Etymology === From Ancient Greek αἰθέριος (aithérios), from αἰθήρ (aithḗr, “upper heaven”). === Noun === etherion (countable and uncountable, plural etherions) (historical) A gas formerly believed to exist in air, initially identified by Charles F. Brush in 1898. He estimated that its density was one ten-thousandth of hydrogen. ==== Related terms ==== ether