scle·ro·sis (skl?-r??s?s)n. pl. scle·ro·ses (-s?z) 1. a. A thickening or hardening of a body part, as of an artery, especially from excessive formation of fibrous interstitial tissue.b. A disease characterized by this thickening or hardening.2. Botany The hardening of cells by the formation of a secondary wall and the deposition of lignin.[Middle English sclirosis, from Medieval Latin scl?r?sis, from Greek skl?r?sis, hardening, from skl?roun, to harden; see scleroma.]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.sclerosis (skl???r??s?s) n, pl -ses (-si?z) 1. (Pathology) pathol a hardening or thickening of organs, tissues, or vessels from chronic inflammation, abnormal growth of fibrous tissue, or degeneration of the myelin sheath of nerve fibres, or (esp on the inner walls of arteries) deposition of fatty plaques. Compare arteriosclerosis, atherosclerosis, multiple sclerosis2. (Botany) the hardening of a plant cell wall or tissue by the deposition of lignin3. a debilitating lack of progress or innovation within an institution or organization[C14: via Medieval Latin from Greek skl?r?sis a hardening] scle?rosal adjCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014scle?ro?sis (skl??ro? s?s) n., pl. -ses (-s?z). 1. a hardening of a body tissue or part, or an increase of connective tissue or the like at the expense of more active tissue. 2. a hardening of a plant tissue or cell wall by thickening or becoming woody. [1350?1400; Middle English