ion

UK: /ˈaɪən/

US: /ˈaɪən, ˈaɪɑn/

US: 'ion': (ī′ən, ī′on); 'Ion': (ī′on)

WordReference Random House Learner's Dictionary of American English © 2025

i•on /ˈaɪən, ˈaɪɑn/   n. 

[countable]
1. an atom or atom group that is electrically charged by the loss or gain of electrons, represented by a plus or a minus sign, as Na⁺, Ca⁺⁺, or Cl^-.

i•on•ic, adj. 

-ion, suffix. 

1. -ion is attached to some roots to form nouns that refer to action or condition:
   uni- (= one) + -ion → union (= condition of being one).

Compare -tion.

WordReference Random House Unabridged Dictionary of American English © 2025

i•on  (ī′ən, ī′on), n. [Physics, Chem.]

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.

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

I•on  (ī′on), n. 

1. Classics, 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. Classics, Literature (italics) a drama on this subject (415? b.c.) by Euripides.

-ion, 

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 esp. past participles (allusion;
   creation;
   fusion;
   notion;
   torsion).

Also, -ation, -ition, -tion. Cf. -cion, -xion. 

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

Ion., 

1. Ionic.

Collins Concise English Dictionary © HarperCollins Publishers::

ion / 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

Etymology: 19th Century: from Greek, literally: going, from ienai to go

Collins Concise English Dictionary © HarperCollins Publishers::

-ion suffix:forming_nouns

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

Etymology: from Latin -iōn-, -io