(music) That which unfolds a single recurrent interval in a series that closes with a return to the initial pitch class.

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

plural of CNO cycle

(astronomy, calendar studies) A particular approximate common multiple of the tropical year and the synodic month; in other words, the 19-year period over which the lunar phases occur on the same dates.

(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.

A large body of prose and verse centering around the traditional heroes of Ulaid and the reign of Conchobar mac Nessa. One of the four major cycles of Irish Mythology.

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.

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

(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.