› [U] NATURAL RESOURCES a chemical element (= simple chemical substance), which exists in all plants and animals, and is an important part of coal and oil. When carbon is burned it produces carbon dioxide and carbon monoxide: All organic substances contain the element carbon. Carbon exists in its pure form as diamond or graphite. carbon atoms › [U] ENVIRONMENT used as a short form for carbon dioxide, especially when talking about the environment and climate change: Car makers are already working hard on reducing carbon. The plan would remove two billion tons of carbon a year from the atmosphere.