ether

1. The medium breathed by human beings; the air. (countable, literary, uncountable)
2. The sky, the heavens; the void, nothingness. (countable, literary, uncountable)
3. Often as aether and more fully as luminiferous aether: The hypothetical substance permeating space, functioning as a medium for electromagnetic waves to propagate through, and which does not exert resistance to the movement of matter; its existence is incompatible with Einstein's theory of relativity; famously found to be undetectable by the 1887 Michelson–Morley experiment. (uncountable)
4. The atmosphere or space as a medium for broadcasting radio and television signals; also, a notional space through which Internet and other digital communications take place; cyberspace. (colloquial, uncountable)
5. A particular quality created by or surrounding an object, person, or place; an atmosphere, an aura. (colloquial, uncountable)
6. Diethyl ether (C₄H₁₀O), an organic compound with a sweet odour used in the past as an anaesthetic. (uncountable)
7. Any of a class of organic compounds containing an oxygen atom bonded to two hydrocarbon groups. (countable)
8. Starting fluid. (uncountable)

Plural ethers