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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 ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

Indo-European & Semitic Roots Appendices

    Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

    Indo-European Roots

    Semitic Roots

    The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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