Noun

(organic compound, countable) A compound containing an oxygen atom bonded to two hydrocarbon groups.

(organic compound, uncountable) Diethyl ether (C₄H₁₀O), a compound used as an early anaesthetic.

(ancient philosophy, and, alchemy, uncountable) A classical physical element, considered as prevalent in the heavens and inaccessible to humans. In some versions of alchemy, this was the fifth element in addition to air, earth, fire and water.

(archaic, physics, uncountable) A substance (aether ) once thought to fill all space that allowed electromagnetic waves to pass through it and interact with matter, without exerting any resistance to matter or energy (disproved by Einstein in his Theory of Relativity).

* {{quote-magazine, date=2013-06-14, author=(Jonathan Freedland)

, volume=189, issue=1, page=18, magazine=(The Guardian Weekly) , title= Obama's once hip brand is now tainted , passage=Now we are liberal with our innermost secrets, spraying them into the public ether with a generosity our forebears could not have imagined. Where we once sent love letters in a sealed envelope, or stuck photographs of our children in a family album, now such private material is despatched to servers and clouds operated by people we don't know and will never meet.}}

The sky or heavens; the upper air.

Noun

(organic compound) The compound with chemical formula C₅H₈O, a cyclic ether used to protect alcohols in organic synthesis.