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[ahy-uh n, ahy-on] /ˈaɪ ən, ˈaɪ ɒn/
noun, Physics, Chemistry.
an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons, as a cation (positive ion) which is created by electron loss and is attracted to the cathode in electrolysis, or as an anion (negative ion) which is created by an electron gain and is attracted to the anode. The valence of an ion is equal to the number of electrons lost or gained and is indicated by a plus sign for cations and a minus sign for anions, thus: Na + , Cl−, Ca ++ , S = .
one of the electrically charged particles formed in a gas by electric discharge or the like.
Origin of ion
< Greek ión going, neuter present participle of iénai to go; term introduced by Michael Faraday in 1834


[ahy-on] /ˈaɪ ɒn/
Classical Mythology. the eponymous ancestor of the Ionians: a son of Apollo and Creusa who is abandoned by his mother but returns to become an attendant in Apollo's temple at Delphi.
(italics) a drama on this subject (415? b.c.) by Euripides.


a suffix, appearing in words of Latin origin, denoting action or condition, used in Latin and in English to form nouns from stems of Latin adjectives (communion; union), verbs (legion; opinion), and especially past participles (allusion; creation; fusion; notion; torsion).
Also, -ation, -ition, -tion.
Compare -cion, -xion.
< Latin -iōn- (stem of -iō) suffix forming nouns, especially on past participle stems; replacing Middle English -ioun < Anglo-French < Latin -iōn-


1. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for ion
Contemporary Examples
Historical Examples
  • ion says that his victory over the Samians wonderfully flattered his vanity.

  • ion records, also, the most successful expression which he used to move the Athenians.

  • His other important novels are ion, dealing with peasant life, and Ciuleandra, a psychological novel.

    Area Handbook for Romania Eugene K. Keefe, Donald W. Bernier, Lyle E. Brenneman, William Giloane, James M. Moore, and Neda A. Walpole
  • ion replies that he is a foreigner, and the Athenians and Spartans will not appoint a foreigner to be their general.

    Ion Plato
  • They were not told what had taken place in their absence, until the day of their return to ion.

    Elsie's New Relations Martha Finley
  • And you, ion, when the name of Homer is mentioned have plenty to say, and have nothing to say of others.

    Ion Plato
  • And when ion heard this he was glad, for he had feared lest haply he should be found to be the son of some slave.

  • Now, ion, will the charioteer or the physician be the better judge of the propriety of these lines?

    Ion Plato
British Dictionary definitions for ion


/ˈaɪən; -ɒn/
an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons See also cation, anion
Word Origin
C19: from Greek, literally: going, from ienai to go


indicating an action, process, or state: creation, objection Compare -ation, -tion
Word Origin
from Latin -iōn-, -io
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
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Word Origin and History for ion

1834, introduced by English physicist and chemist Michael Faraday (suggested by the Rev. William Whewell, English polymath), coined from Greek ion, neuter present participle of ienai "go," from PIE root *ei- "to go, to walk" (cf. Greek eimi "I go;" Latin ire "to go," iter "a way;" Old Irish ethaim "I go;" Irish bothar "a road" (from *bou-itro- "cows' way"), Gaulish eimu "we go," Gothic iddja "went," Sanskrit e'ti "goes," imas "we go," ayanam "a going, way;" Avestan ae'iti "goes;" Old Persian aitiy "goes;" Lithuanian eiti "to go;" Old Church Slavonic iti "go;" Bulgarian ida "I go;" Russian idti "to go"). So called because ions move toward the electrode of opposite charge.


suffix forming nouns of state, condition, or action from verbs, from Latin -ionem (nominative -io), sometimes via French -ion.

Online Etymology Dictionary, © 2010 Douglas Harper
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ion in Medicine

ion i·on (ī'ən, ī'ŏn')
An atom or a group of atoms that has acquired a net electric charge by gaining or losing one or more electrons.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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ion in Science
  (ī'ən, ī'ŏn')   
An atom or a group of atoms that has an electric charge. Positive ions, or cations, are formed by the loss of electrons; negative ions, or anions, are formed by the gain of electrons.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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ion in Culture
ion [(eye-uhn, eye-on)]

An atom that has either lost or gained one or more electrons, so that it has an electrical charge. Ions can be either positively or negatively charged.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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