Calvin cyclen. A series of chemical reactions that occur as part of photosynthesis, in which carbon is broken away from gaseous carbon dioxide and fixed as organic carbon in compounds that are ultimately converted into sugars.[After Melvin Calvin.]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.Calvin cycle n (Botany) botany a series of reactions, occurring during photosynthesis, in which glucose is synthesized from carbon dioxide [C20: named after Melvin Calvin, who elucidated it]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014