[mod.L., a. Gr. ἐξόστωσις (Galen) outgrowth of bone, f. ἐξ (see EX- pref.2) + ὀστέον bone.]
1. Path. a. The formation of bone on another bone, or on some other structure in the body. b. concr. A bony tumor found upon a bone or cartilage.
a. 1804. Abernethy, Surg. Obs., 32. Tumours growing near, and compressing the surface of bones, frequently occasion a degree of exostosis.
b. 1736. Freke, in Phil. Trans., XLI. 369. It may be said to come under the Denomination of an Exostosis.
1782. W. Heberden, Comm. Hist. & Cure Dis. (1806), xi. 68. Except some exostoses of the vertebræ of the thorax.
1839. Todd, Cycl. Anat., II. 220/2. Exostosis appears most frequently on the upper jaw.
1868. Darwin, Anim. & Pl., II. xii. 23. Bony exostoses on the legs [of a horse] caused by too much travelling on hard roads.
2. Bot. ‘A diseased condition in plants, in which hard masses of wood are produced, projecting like warts or tumours from the main stem or roots’ (Treas. Bot., 1866).
