Keratin

n. (Biology) protein substance which is found in horn (also in nails, hair, hoofs, etc.)

Keratins are a family of fibrous structural proteins; tough and insoluble, they form the hard but nonmineralized structures found in reptiles, birds, amphibians and mammals. They are rivaled as biological materials in toughness only by chitin.There are various types of keratins within a single animal.
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Keratin /ker·a·tin/ any of a family of scleroproteins that are the main constituents of epidermis, hair, nails, and horny tissues. [more]Keratin - Community and Resources

Noun
1. a fibrous scleroprotein that occurs in the outer layer of the skin and in horny tissues such as hair feathers nails and hooves
(synonym) ceratin
(hypernym) scleroprotein, albuminoid
(substance-holonym) horn

n. keratin, protein substance which is found in horn (also in nails, hair, hoofs, etc.) (Biology)