ceratin - a fibrous scleroprotein that occurs in the outer layer of the skin and in horny tissues such as hair feathers nails and hoovesfeather, plumage, plume - the light horny waterproof structure forming the external covering of birds hair - dense growth of hairs covering the body or parts of it (as on the human head); helps prevent heat loss; "he combed his hair" horn - the material (mostly keratin) that covers the horns of ungulates and forms hooves and claws and nails |