carbon cycle

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Physics See carbon-nitrogen cycle.
2. n. 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.

Wiktionary

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

WordNet 3.0

1. n. a thermonuclear reaction in the interior of stars
2. n. the organic circulation of carbon from the atmosphere into organisms and back again