n.1 an abnormal hardening of body tissue (see also ARTERIOSCLEROSIS, ATHEROSCLEROSIS).
2 (in full multiple or disseminated sclerosis) a chronic and progressive disease of the nervous system resulting in symptoms including paralysis and speech defects.
3 Bot. the hardening of a cell-wall with lignified matter.
Etymology: ME f. med.L f. Gk sklerosis f. skleroo harden