plas·min (pl?z?m?n)n. A proteolytic enzyme that is formed from plasminogen in blood plasma and dissolves the fibrin in blood clots. Also called fibrinolysin.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.plasmin (?plæzm?n) n (Biochemistry) a proteolytic enzyme that causes fibrinolysis in blood clotsCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014plas?min (?plæz m?n) n. an enzyme in the blood that dissolves blood clots by breaking down fibrin. Also called fibrinolysin. [1865?70] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.