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  • ion
    ion
    noun
    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 = .
  • Ion
    Ion
    noun
    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.
  • -ion
    -ion
    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 ).
  • Ion.
    Ion.
    abbreviation
    Ionic.
SEE ALSO:
Slang dictionary results for ion.

ion

1 American  
[ahy-uhn, ahy-on] / ˈaɪ ən, ˈaɪ ɒn /

noun

Physics, Chemistry.
  • ions
    plural

  1. 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 = .

  2. one of the electrically charged particles formed in a gas by electric discharge or the like.

Ion 2 American  
[ahy-on] / ˈaɪ ɒn /

noun

  1. 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.

  2. (italics) a drama on this subject (415? b.c.) by Euripides.

-ion 3 American  

  1. 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 ).

Ion. 4 American  

abbreviation

  1. Ionic.

ion 1 British  
/ ˈaɪən, -ɒn /

noun

  1. an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons See also cation anion

"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
-ion 2 British  

suffix

  1. indicating an action, process, or state Compare -ation -tion

    creation

    objection
"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
ion Scientific  
/ ī′ən,ī′ŏn′ /

  1. 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.

ion Cultural  

  1. 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.

Other Word Forms

Noun Inflected Forms

Etymology

Origin of ion1

< Greek ión going, neuter present participle of iénai to go; term introduced by Michael Faraday in 1834

Origin of -ion3

< Latin -iōn- (stem of -iō ) suffix forming nouns, especially on past participle stems; replacing Middle English -ioun < Anglo-French < Latin -iōn-

Explanation

An ion is an atom or particle with a positive or negative electrical charge. Think of an ion as having a plus or minus sign. Ion is a word you are most likely to encounter in a physics or chemistry text. But you don’t have to be a chemist or physicist to understand the concept. If you had a neutral particle and you were able to remove or add an electron, then you would have an ion — a charged particle. Don't confuse the tiny ion with the similar word eon, which is an extremely long period of time.

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Vocabulary lists containing ion

Electricity and Magnetism - Introductory

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Structure and Properties of Matter - Middle School

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Chemistry: Structure and Properties of Matter

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Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

See Examples For:

The electrically charged atom was held nearly motionless in an ion trap, which uses electromagnetic fields to keep the ion fixed in place.

From Science Daily ● Sep. 13, 2026

At first glance, it seems reasonable to expect that an ion would interact most strongly with a laser exactly at the beam's brightest point.

From Science Daily ● Sep. 13, 2026

For the first time, researchers have experimentally demonstrated the optical Magnus effect by focusing laser light on a single ion and measuring how the light interacts with it.

From Science Daily ● Sep. 13, 2026

Instead of causing an atom to follow a curved path, the effect shifts the location where the laser interacts most strongly with the ion.

From Science Daily ● Sep. 13, 2026

"Technically," she corrected, "the booster only took me into orbit. It was the nuclear-powered ion engine that took me to Mars."

From "The Martian" by Andy Weir

The need for such high levels of reliability can stress the capabilities of AI architectures and humans alike, according to computer scientist and Databricks co-founder Ion Stoica.

From The Wall Street Journal ● Jun. 25, 2026

Ion is tailored for procedures in the lung, typically to sample suspicious nodules or legions as part of a cancer diagnosis.

From Barron's ● Apr. 21, 2026

Games will also air on Ion and USA Network.

From Los Angeles Times ● Mar. 18, 2026

Ion channels are tiny openings that control the movement of charged particles in living organisms.

From Science Daily ● Feb. 19, 2026

“Oh,” Ion cried, “my mother must have put them around me. They are a clue to my mother. I will seek her everywhere—through Europe and through Asia.”

From "Mythology: Timeless Tales of Gods and Heroes" by Edith Hamilton

In the first place, the Portuguese, who discovered that island in 1506, and explored its coasts in the following years, could not have Ion. remained in ignorance of De Gonneville's voyage.

From The History of Australian Exploration from 1788 to 1888 by Ernest Favenc

They found that calcium ions initiate the contraction, while an unusual fishnet-like structure carries out the movement.

From Science Daily ● Sep. 19, 2026

Trapped ions are also widely used in quantum computing.

From Science Daily ● Sep. 13, 2026

As crystals develop, their ions need enough freedom to rearrange before settling into their final positions.

From Science Daily ● Aug. 30, 2026

"These structures can be systematically doped with silver and other ions and engineered to interface seamlessly with perovskites -- transforming DNA from a biological macromolecule into a programmable, multifunctional nanomaterials platform."

From Science Daily ● Aug. 17, 2026

Francis, as well as I, knew almost nothing about how inorganic ions were arranged in three dimensions.

From "Double Helix" by James D. Watson

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.

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