cy·clone (s??kl?n?)n.1. Meteorology a. An atmospheric system characterized by the rapid inward circulation of air masses about a low-pressure center, usually accompanied by stormy, often destructive weather. Cyclones circulate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.b. A violent tropical storm, especially one originating in the southwestern Pacific Ocean or Indian Ocean.2. A violent rotating windstorm, especially a tornado.3. Any of various devices using centrifugal force to separate materials.[From Greek kukl?n, present participle of kukloun, to rotate, from kuklos, circle; see kwel- in Indo-European roots.]cy·clon?ic (-kl?n??k), cy·clon?i·cal adj.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.