(biochemistry) A series of enzymatic reactions that occurs in all aerobic organisms; it involves the oxidative metabolism of acetyl units, and serves as the main source of cellular energy.

the cycle of water from the oceans to the atmosphere to land and back into the oceans or atmosphere.

The natural circulation of nitrogen, in which atmospheric nitrogen is converted to nitrogen oxides by lightning and deposited in the soil by rain, where it is assimilated by plants and either eaten by animals (and returned as faeces) or decomposed back to elemental nitrogen by bacteria.

(biology) The course of stages through which an organism passes from fertilized zygote until maturity, reproduction, and death.

(Irish mythology) A body of prose and verse focusing on the exploits of the mythological hero Fionn mac Cumhail and his warriors the Fianna Éireann.

(biology) the transmission of hydrogen from water to carbohydrates etc and back to water by living organisms

carbon-nitrogen-oxygen cycle

The basic thermodynamic cycle of the normal four-stroke internal combustion engine: isentropic compression, constant-volume heat addition, isentropic expansion, and constant-volume heat rejection.

(business) The business cycle from startup of operations to the profit; from obtaining the raw material, through designing and production, to the distribution and profits.

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