sclerosis

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A thickening or hardening of a body part, as of an artery, especially from excessive formation of fibrous interstitial tissue.
• noun A disease characterized by this thickening or hardening.
• noun Botany The hardening of cells by the formation of a secondary wall and the deposition of lignin.

from The Century Dictionary.

• noun A hardening or induration; specifically, the increase of the sustentacular tissue (neuroglia, or connective tissue) of a part at the expense of the more active tissue.
• noun In botany, the induration of a tissue or cell-wall either by thickening of the membranes or by their lignification (that is, by the formation of lignin in them).

from the GNU version of the Collaborative International Dictionary of English.

• noun (Med.) Induration; hardening; especially, that form of induration produced in an organ by increase of its interstitial connective tissue.
• noun (Bot.) Hardening of the cell wall by lignification.
• noun (Med.) an affection in which patches of hardening, produced by increase of the neuroglia and atrophy of the true nerve tissue, are found scattered throughout the brain and spinal cord. It is associated with complete or partial paralysis, a peculiar jerking tremor of the muscles, headache, and vertigo, and is usually fatal. Formerly referred to as multiple sclerosis, disseminated sclerosis, or insular sclerosis, but now usually called only multiple sclerosis, or MS.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun pathology The abnormal hardening of body tissues, such as an artery.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any pathological hardening or thickening of tissue