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.

(physics) A thermodynamic cycle used as an ideal standard for the comparative performance of heat engines.

The recurring cycle of physiological changes in the uninseminated females of some animal species that is associated with reproductive fertility; especially the cycle in a human woman.

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

Alternative spelling of sulfur cycle

(chemistry, biochemistry) the natural cycle which includes the mineralization of organic sulfur to sulfide, oxidation of this to sulfate, and reduction of this to sulfide followed by microbial incorporation of this into organic compounds

plural of CNO cycle

Alternative form of vicious circle

(systems theory) A closed trajectory in phase space of a dynamical system having the property that at least one other trajectory spirals into it either as time approaches infinity or as time approaches minus-infinity.