Cycle. From the Greek Kuklos. The ancients divided time into end less cycles, wheels within wheels, all such periods being of various durations, and each marking the beginning or the end of some event either cosmic, mundane, physical or metaphysical. There were cycles of only a few years, and cycles of immense duration, the great Orphic cycle, referring to the ethnological change of races, lasting 120,000 years, and the cycle of Cassandrus of 136,000, which brought about a complete change in planetary influences and their correlations between men and gods—a fact entirely lost sight of by modern astrologers.
Source: H.P.Blavatsky - The Theosophical Glossary