ether

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of a class of organic compounds in which two hydrocarbon groups are linked by an oxygen atom.
• noun A volatile, highly flammable liquid, C₄H₁₀O, derived from distilling ethyl alcohol with sulfuric acid, used as a reagent and solvent, and formerly used as an anesthetic.
• noun The regions of space beyond the earth's atmosphere; the heavens.
• noun The element believed in ancient and medieval civilizations to fill all space above the sphere of the moon and to compose the stars and planets.
• noun Physics An all-pervading, infinitely elastic, massless medium formerly postulated as the medium of propagation of electromagnetic waves.

from The Century Dictionary.

• An obsolete form of either.
• A dialectal variant of edder.
• noun A dialectal form of adder.
• noun The upper air; the blue heavens. It was supposed by Aristotle to extend from the fixed stars down to the moon.
• noun In astronomy and physics, a hypothetical medium of extreme tenuity and elasticity supposed to be diffused throughout all space (as well as among the molecules of which solid bodies are composed), and to be the medium of the transmission of light and heat. See the extract.
• noun In chem.: One of a class of organic bodies divided into two groups: Simple ethers, consisting of two basic hydrocarbon radicals united by oxygen, and corresponding in constitution to the metallic oxids, as CH₃OCH₃, methylether, or methyloxid, analogous to AgOAg, silver oxid. Compound ethers, consisting of one or more basic or alcohol radicals and one or more acid hydrocarbon radicals united by oxygen, and corresponding to salts of the metals, as CH₃COO C₂H₅, ethyl acetate, or acetic ether, corresponding to CH₃COONa, sodium acetate. Also called esters
• noun Specifically, ethyl oxid or ethyl ether (C₂H₅)₂O, also called, but improperly, sulphuric ether, because prepared from a mixture of sulphuric acid and alcohol.
• noun See the adjectives.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Physics) A medium of great elasticity and extreme tenuity, once supposed to pervade all space, the interior of solid bodies not excepted, and to be the medium of transmission of light and heat; hence often called luminiferous ether. It is no longer believed that such a medium is required for the transmission of electromagnetic waves; the modern use of the term is mostly a figurative term for empty space, or for literary effect, and not intended to imply the actual existence of a physical medium. However. modern cosmological theories based on quantum field theory do not rule out the possibility that the inherent energy of the vacuum is greater than zero, in which case the concept of an ether pervading the vacuum may have more than metaphoric meaning.
• noun Supposed matter above the air; the air itself.
• noun A light, volatile, mobile, inflammable liquid, (C2H5)2O, of a characteristic aromatic odor, obtained by the distillation of alcohol with sulphuric acid, and hence called also sulphuric ether. It is a powerful solvent of fats, resins, and pyroxylin, but finds its chief use as an anæsthetic. Commonly called ethyl ether to distinguish it from other ethers, and also ethyl oxide.
• noun Any similar compound in which an oxygen atom is bound to two different carbon atoms, each of which is part of an organic radical
• noun (Chem.) an ether in which the ether oxygen is attached to two radicals having different structures; as, ethyl methyl ether, C2H5.O.CH3.
• noun (Chem.) an ethereal salt or a salt of some hydrocarbon as the base; an ester.
• noun (Mach.) a condensing engine like a steam engine, but operated by the vapor of ether instead of by steam.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun organic chemistry, countable A compound containing an oxygen atom bonded to two hydrocarbon groups.
• noun organic chemistry, uncountable Diethyl ether (C4H10O), a compound used as an early anaesthetic.
• noun 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.
• noun 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).
• noun The sky or heavens; the upper air.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of a class of organic compounds that have two hydrocarbon groups linked by an oxygen atom
• noun a medium that was once supposed to fill all space and to support the propagation of electromagnetic waves
• noun the fifth and highest element after air and earth and fire and water; was believed to be the substance composing all heavenly bodies
• noun a colorless volatile highly inflammable liquid formerly used as an inhalation anesthetic