ion

¹ American  

[ahy-uhn, ahy-on] / ˈaɪ ən, ˈaɪ ɒn /

noun

Physics, Chemistry.

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.

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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.

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-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 ).

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Ion. ⁴ American  

abbreviation

1. Ionic.

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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

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-ion ² British  

suffix

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

   creation

   objection

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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.

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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.

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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.

Example Sentences

The company designs and manufactures ion implantation equipment that is critical in creating transistors on chips.

From MarketWatch • Mar. 28, 2026

Still, Dorsheimer said the impending merger with Veeco “will complement Axcelis’s singular focus on ion implant and cast a wider net to cover semiconductor capital equipment.”

From MarketWatch • Mar. 28, 2026

"I've worked on many ion channels, and TMEM175 is by far the strangest of them all," says Dr. Oliver Rauh, who moved from TU Darmstadt to H-BRS to work in the research collaboration CytoTransport.

From Science Daily • Mar. 26, 2026

Researchers have uncovered how a mysterious ion channel helps cells break down waste, opening new possibilities for treating Parkinson's disease.

From Science Daily • Mar. 26, 2026

It was the only time that Vhaghar, Meraxes, and Baler- ion were all unleashed at once.

From "A Game of Thrones" by George R.R. Martin