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 = .
one of the electrically charged particles formed in a gas by electric discharge or the like.
1834, introduced by Eng. physicist and chemist Michael Faraday (suggested by the Rev. William Whewell, Eng. polymath), coined from Gk. ion, neut. prp. of ienai "go," from PIE base *ei- "to go, to walk" (cf. Gk. eimi "I go;" L. ire "to go," iter "a way;" O.Ir. ethaim "I go;" Ir. bothar "a road" (from *bou-itro- "cows' way"), Gaulish eimu "we go," Goth. iddja "went," Skt. e'ti "goes," imas "we go," ayanam "a going, way;" Avestan ae'iti "goes;" O.Pers. aitiy "goes;" Lith. eiti "to go;" O.C.S. iti "go;" Bulgarian ida "I go;" Rus. idti "to go"). So called because ions move toward the electrode of opposite charge. Ionosphere coined 1926 by R.A. Watson-Watt.