Definitions for ions
U.S. National Library of Medicine
An atom or group of atoms that have a positive or negative electric charge due to a gain (negative charge) or loss (positive charge) of one or more electrons. Atoms with a positive charge are known as CATIONS; those with a negative charge are ANIONS.
The Standard Electrical Dictionary
The products of decomposition produced in any given electrolysis are termed ions, the one which appears at the anode or negative electrode is the anion. The electrode connected to the carbon or copper plate of a wet battery is an anode. Thus in the electrolysis of water oxygen is the anion and hydrogen is termed the kation. In this case both anion and kation are elements. In the decomposition of copper sulphate the anion is properly speaking sulphion (S O4), a radical, and the kation is copper, an element. Electro-negative elements or radicals are anions, such as oxygen, sulphion, etc., while electro-positive ones are kations, such as potassium. Again one substance may be an anion referred to one below it and a kation referred to one above it, in the electro-chemical series, q. v. Anion means the ion which goes to the anode or positive electrode; kation, the ion which goes to the kathode or negative electrode. [Transcriber's note: An ion is an atom or molecule that has lost or gained one or more valence electrons, giving it a positive or negative electrical charge. A negatively charged ion, with more electrons than protons in its nuclei, is an anion. A positively charged ion, with fewer electrons than protons, is a cation. The electron was discovered five years after this publication.]