Retained name
In chemistry, a retained name is an established name for a chemical compound that is recommended for use by a system of chemical nomenclature (for example, IUPAC nomenclature), but that is not exactly, or not at all, systematic. Retained names are often used for the most fundamental parts of a nomenclature system: almost all the chemical elements have retained names rather than being named systematically, as do the first four alkanes, benzene and most simple heterocyclic compounds.