The Collaborative International Dictionary of English v.0.48:

Sclerosis \Scle*ro"sis\, n. [NL., fr. Gr. (??, fr. sklhro`s
   hard.]
   1. (Med.) Induration; hardening; especially, that form of
      induration produced in an organ by increase of its
      interstitial connective tissue.
      [1913 Webster]

   2. (Bot.) Hardening of the cell wall by lignification.
      [1913 Webster]

   Cerebro-spinal sclerosis (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.
      [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

sclerosis
    n 1: any pathological hardening or thickening of tissue [syn:
         sclerosis, induration]

Moby Thesaurus II by Grady Ward, 1.0:

165 Moby Thesaurus words for "sclerosis":
   abscess, ague, anemia, angina, angina pectoris, ankylosis, anoxia,
   aortic insufficiency, aortic stenosis, apnea, apoplectic stroke,
   apoplexy, arrhythmia, arteriosclerosis, asphyxiation, asthma,
   ataxia, atherosclerosis, atrial fibrillation, atrophy,
   auricular fibrillation, backache, beriberi heart, bleeding,
   blennorhea, cachexia, cachexy, calcification, callusing,
   cardiac arrest, cardiac insufficiency, cardiac shock,
   cardiac stenosis, cardiac thrombosis, carditis, case hardening,
   chill, chills, colic, concretion, congenital heart disease,
   constipation, convulsion, cor biloculare, cor juvenum,
   cor triatriatum, cornification, coronary, coronary insufficiency,
   coronary thrombosis, coughing, crystallization, cyanosis, diarrhea,
   diastolic hypertension, dizziness, dropsy, dysentery, dyspepsia,
   dyspnea, edema, emaciation, encased heart, endocarditis,
   extrasystole, fainting, fatigue, fatty heart, fever, fibrillation,
   fibroid heart, firming, flask-shaped heart, flux, fossilization,
   frosted heart, granulation, growth, hairy heart, hardening,
   heart attack, heart block, heart condition, heart disease,
   heart failure, hemorrhage, high blood pressure, hornification,
   hydrops, hypertension, hypertensive heart disease, hypotension,
   icterus, indigestion, induration, inflammation, insomnia,
   ischemic heart disease, itching, jaundice, labored breathing,
   lapidification, lithification, low blood pressure, lumbago,
   marasmus, mitral insufficiency, mitral stenosis,
   myocardial infarction, myocardial insufficiency, myocarditis,
   myovascular insufficiency, nasal discharge, nausea, necrosis,
   ossification, ox heart, pain, palpitation, paralysis,
   paralytic stroke, paroxysmal tachycardia, pericarditis,
   petrifaction, petrification, pile, premature beat, pruritus,
   pseudoaortic insufficiency, pulmonary insufficiency,
   pulmonary stenosis, rash, rheum, rheumatic heart disease,
   round heart, seizure, setting, shock, skin eruption, sneezing,
   solidification, sore, spasm, steeling, stiffening, stony heart,
   stroke, tabes, tachycardia, tempering, thrombosis, toughening,
   tricuspid insufficiency, tricuspid stenosis, tumor, turtle heart,
   upset stomach, varicose veins, varix, ventricular fibrillation,
   vertigo, vitrifaction, vitrification, vomiting, wasting