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e·ther (ēthər)
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n.
1. Any of a class of organic compounds in which two hydrocarbon groups are linked by an oxygen atom.
2. 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. Also called diethyl ether, ethyl ether.
3. The regions of space beyond the earth's atmosphere; the heavens.
4. 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.
5. Physics An all-pervading, infinitely elastic, massless medium formerly postulated as the medium of propagation of electromagnetic waves.

[Middle English, upper air, from Latin aethēr, from Greek aithēr.]

e·theric (ĭ-thĕrĭk, ĭ-thîr-) adj.

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2017 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

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