\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

His big commitment to lithium-ion technology is tantamount to a bet that no battery breakthroughs are in the offing to fix the range and charging drawbacks that are the main handicap of electric vehicles. Holman W. Jenkins, WSJ, "The Last Temptation of Elon Musk," 22 May 2018 If there are an equal number of hydrogen and hydroxide ions present, the acid and base will neutralize each other, forming a salt and water. Megan Arnett, Scientific American, "Sweet and Sour Science You Can Taste!," 21 June 2018 That movement of ions is the basis for many of the body’s functions, like nerve impulses, muscle contractions and digestion. Katie Thomas, New York Times, "Jens Christian Skou, Nobel Winner for Chemistry, Dies at 99," 1 June 2018 The lithium-ion cells caught fire again after the vehicle was taken to a storage yard. Fortune, "Tesla That Caught Fire in Florida Crash Reached 116 MPH," 26 June 2018 The vehicle’s 400-volt lithium-ion high-voltage battery was breached in the crash, leading to a fire, investigators said. Mike Spector, WSJ, "Tesla Autopilot System Warned Driver to Put Hands on Wheel, U.S. Investigators Say," 7 June 2018 All lithium-ion smartphone batteries work this that way. Jennifer Jolly, USA TODAY, "What to do now if your iPhone's battery still won't make it through the day," 25 Apr. 2018 There's also a kit for wrenches, a 1/2-Inch High-Torque Impactool, Charger, 2 Li-ion Batteries and Case Kit. David Grossman, Popular Mechanics, "These Cheap Impact Wrenches Will Give Your Toolbox Some Serious Power," 17 Oct. 2017 Previous versions of the protein worked sluggishly to move ions in and out of neurons — a critical step in generating electrical signals to the brain conveying the rapidly changing characteristics of sound like loudness and pitch. Justin Chen, STAT, "Pulses of light restored hearing in gerbils. Could that lead to higher-tech cochlear implants?," 11 July 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





Statistics for ion

Last Updated

5 Oct 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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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).


not any or not one

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