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[an-ahy-uh n]
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noun Physical Chemistry.
  1. a negatively charged ion, as one attracted to the anode in electrolysis.
  2. any negatively charged atom or group of atoms (opposed to cation).
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Origin of anion

1825–35; < Greek, neuter of aniṓn going up (present participle of aniénai to go up), equivalent to an- an-3 + -i- go + -ōn present participle suffix
Related formsan·i·on·ic [an-ahy-on-ik] /ˌæn aɪˈɒn ɪk/, adjectivean·i·on·i·cal·ly, adverb
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for anion

Historical Examples

  • One of these is always composed of oxygen and hydrogen and is the anion.

    An Elementary Study of Chemistry

    William McPherson

  • Now, one question: Has the news of the death of the ram of Anion reached you?

    Uarda, Complete

    Georg Ebers

  • The king repaired in state to the temple of Anion, seized the priests who professed these seditious beliefs, and burnt them alive.

  • The Nile beyond surrounded an island, where flourished the well-kept sacred grove of Anion.

    Uarda, Complete

    Georg Ebers

  • In a few minutes the priest of Anion and the chief of the kolchytes were being carried towards the valley in their litters.

    Uarda, Complete

    Georg Ebers

British Dictionary definitions for anion


  1. a negatively charged ion; an ion that is attracted to the anode during electrolysisCompare cation
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Derived Formsanionic (ˌænaɪˈɒnɪk), adjective

Word Origin

C19: from ana- + ion
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for anion


"a negatively charged ion, which moves toward the anode (q.v.) during electrolysis," 1834, proposed by the Rev. William Whewell (1794-1866), English polymath, and published by English physicist Michael Faraday, from Greek anion "(thing) going up," neuter past participle of anienai "go up," from ana "up" (see ana-) + ienai "go" (see ion).

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Online Etymology Dictionary, © 2010 Douglas Harper

anion in Medicine


  1. A negatively charged ion, especially one that migrates to the anode in electrolysis.
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Related formsani•onic (-ŏnĭk) adj.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

anion in Science


  1. An ion with net negative charge, having more electrons than protons. In electrolysis, anions migrate to a positively charged anode. Compare cation.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.