noun. The proper substance of horn or horny tissue; the organic substance of the ceratina, entering largely into the composition of epithelial or cuticular structures, as horns, hoofs, nails, etc. Also keratin, keratine.

noun. a fibrous scleroprotein that occurs in the outer layer of the skin and in horny tissues such as hair, feathers, nails, and hooves

"Our present system of modes of production and modes of exchanges of goods and services (distribution), and the relationships between them, continue to be described (seldom defined) as a form of “ism,” based on descriptive terms applied to ceratin of its elements by antagonists of the system, such as Karl Marx."

albuminoid  scleroprotein  

certain  certain, keratin  keratin