During the Ontologies4Chem workshop organized by NFDI4Chem in September 2022, the idea arose to use The Compendium of Chemical Terminology (colloquially known as the "Gold Book") as a canonical source for the definition of chemical ontology terms. The Gold Book, first published in 1987 by the International Union of Pure and Applied Chemistry (IUPAC), is the definitive guide to formally defined chemical terminology and is considered the authoritative source of expert knowledge based on scientific discourse and a thorough review and consensus process in the chemistry domain. The Gold Book can thus help in the development of chemical ontologies by providing an expert consensus based on the meaning of technical terms from which ontology terms can be derived. For this reason, when defining a new (chemical) term in an ontology, it is always advisable to first check whether a valid definition already exists in the Gold Book that can be used for this purpose.