ly·sis (l??s?s)n. pl. ly·ses (-s?z) 1. Biochemistry The dissolution or destruction of cells, such as blood cells or bacteria, as by the action of a specific lysin that disrupts the cell membrane.2. Medicine The gradual subsiding of the symptoms of an acute disease.[New Latin, from Latin, a loosening, from Greek lusis, from l?ein, to loosen; see leu- in Indo-European roots.]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.lysis (?la?s?s) n, pl -ses (-si?z) 1. (Biochemistry) the destruction or dissolution of cells by the action of a particular lysin2. (Medicine) med the gradual reduction in severity of the symptoms of a disease[C19: New Latin, from Greek, from luein to release]Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014ly?sis (?la? s?s) n. 1. the dissolution or destruction of cells by lysins. 2. the gradual recession of a disease. Compare crisis (def. 4). [1815?25;