zy·mo·gen (z??m?-j?n)n. See proenzyme.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.zymogen (?za?m???d??n) n (Biochemistry) biochem any of a group of compounds that are inactive precursors of enzymes and are activated by a kinaseCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014zy?mo?gen (?za? m? d??n, -?d??n) n. any of various enzyme precursor molecules that may change into an enzyme as a result of catalytic change. Also called proenzyme. [