(ī′ən, ī′on) noun Physics
1. An electrically charged atom, radical, or molecule, formed by the dissolution of an electrolyte and becoming a cation with a positive (+) charge if electrons are lost, or an anion with a negative (-) charge if electrons are gained. Thus, a molecule of sodium chloride, NaCl, in aqueous solution, dissociates into the sodium cation Na⁺, with a deficiency of one electron, and the chlorine anion Cl^–, with an excess of one electron.
2. In a gas, an electrified particle produced in various ways, as by the action of an electric current or of rays such as the ultraviolet and certain radium emanations. See HYDROGEN ION. [<Gk. ion, neut. of iōn, ppr. of ienai go]

1. Action or process of: communion.
2. Condition or state of being: union.
3. Result of: opinion. Also –ation, –tion. [<F ion <L -io, -ionis]