carbon cycle

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Ecology The combined processes, including photosynthesis, decomposition, and respiration, by which carbon as a component of various compounds cycles between its major reservoirs—the atmosphere, oceans, and living organisms.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun the physical cycle of carbon through the Earth’s biosphere, geosphere, hydrosphere and atmosphere that includes such processes as photosynthesis, decomposition, respiration and carbonification.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a thermonuclear reaction in the interior of stars
• noun the organic circulation of carbon from the atmosphere into organisms and back again