Sclerosis

[sklɪə'rəʊsɪs;sklə-] or [sklə'rosɪs]

(noun.) any pathological hardening or thickening of tissue.

Checked by Anita--From WordNet

(n.) Induration; hardening; especially, that form of induration produced in an organ by increase of its interstitial connective tissue.

(n.) Hardening of the cell wall by lignification.

Checker: Newman