\ˈī-ən, ˈī-ˌän\

Definition of ion 

(Entry 1 of 3)

1 : an atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons

2 : a charged subatomic particle (such as a free electron)

Definition of Ion (Entry 2 of 3)


Definition of -ion (Entry 3 of 3)

1a : act or process validation

b : result of an act or process regulation

2 : state or condition hydration

Examples of ion in a Sentence

Recent Examples on the Web: Noun

The most commonly used batteries, lithium-ion, store energy in solid materials, like various metals. Angela Chen, The Verge, "How a ‘solar battery’ could bring electricity to rural areas," 27 Sep. 2018 In a vacuum, Harvard University physicist Lene Hau created a tiny cloud of sodium ions so cold that their movements synchronized. Popular Mechanics, "Could You Design a Box That Traps Light Inside of It?," 17 Sep. 2018 Cranking the arm generates a magnetic field that’s able to charge the lithium ion battery inside tube. Liz Stinson, Curbed, "Nendo designs an attractive hand-crank phone charger," 12 Nov. 2018 Water can act as either an acid or a base filled with both hydrogen and hydroxide ions. David Grossman, Popular Mechanics, "A New Hydrophobic Surface Could Turn the Ocean's Waves Into Electricity," 4 Oct. 2018 By now our battery week coverage has made clear that lithium ion batteries aren’t radically evolving or getting replaced anytime soon. Chris Welch, The Verge, "The best battery packs for carrying everywhere and charging everything," 17 Aug. 2018 The colors of the flowers are affected by the aluminum ions in the soil. Micaela English, Town & Country, "13 Facts Every Hydrangea Enthusiast Needs To Know," 30 Mar. 2015 For example, one method uses special membrane filters to separate the hydrogen and hydroxide ions produced during electrolysis. Scott K. Johnson, Ars Technica, "Splitting water for fuel while removing CO₂ from the air," 28 June 2018 Hadfield tentatively suggested that ion propulsion, nuclear power, or even the manipulation of gravity might be safer. David Z. Morris, Fortune, "This Retired Astronaut Says SpaceX and NASA Rockets 'Will Never Go to Mars'," 17 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'ion.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of ion


circa 1834, in the meaning defined at sense 1

History and Etymology for ion


Greek, neuter of iōn, present participle of ienai to go — more at issue entry 1

Noun suffix

French -ion, from Latin -ion-, -io

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Dictionary Entries near ion


Io moth





ion chamber

Statistics for ion

Last Updated

30 Nov 2018

Look-up Popularity

Time Traveler for ion

The first known use of ion was circa 1834

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More Definitions for ion



English Language Learners Definition of ion

 (Entry 1 of 2)

: an atom or group of atoms that has a positive or negative electric charge from losing or gaining one or more electrons

English Language Learners Definition of -ion (Entry 2 of 2)

: act or process

: result of an act or process

: state or condition


\ˈī-ən, ˈī-ˌän\

Kids Definition of ion

: an atom or group of atoms that carries an electric charge

Kids Definition of -ion

1 : act or process construction

2 : result of an act or process regulation eruption

3 : state or condition perfection


\ˈī-ən, ˈī-ˌän \

Medical Definition of ion 

1 : an atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons — see anion, cation

2 : a charged subatomic particle (as a free electron)

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More from Merriam-Webster on ion

Rhyming Dictionary: Words that rhyme with ion

Spanish Central: Translation of ion

Nglish: Translation of ion for Spanish Speakers

Britannica English: Translation of ion for Arabic Speakers Encyclopedia article about ion

Comments on ion

What made you want to look up ion? Please tell us where you read or heard it (including the quote, if possible).


the figure or shape of a crescent moon

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