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.

(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

Alternative spelling of sulfur cycle

(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.

(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.

The natural cycle of evaporation of water from the oceans etc, and subsequent condensation and precipitation as rain and snow

(physiology) The cycle of the thickening of the uterine lining in anticipation of an embryo implantation.

(physiology) The cycle associated with the maturation of the oocyte and its discharge from the ovary, from where it passes through the oviduct to the uterus.