Definition of the word dioxide

The word "dioxide" derives from two Greek roots: "dio," meaning two, and "oxys," meaning acid-forming. In ancient chemistry, oxygen was labeled "di-acid," as it was found to have the ability to combine with two parts of a substance, hence "dioxys." As oxygen was further studied, its compound forms with other elements began to be recognized. Compounds in which oxygen combines with other elements to form two oxygen atoms were labeled "dioxides." The term has since been applied to a wide variety of inorganic and organic compounds, such as carbon dioxide (CO2), sulfur dioxide (SO2), and nitrogen dioxide (NO2), all of which are important in a variety of industrial and environmental processes.