The crossword solution for the term 'Protein in Horns and Hair' is Keratin. Keratin is a fibrous protein that is the main structural component of hair, nails, horns, claws, hooves, and the outer layer of skin in mammals. It is also found in the feathers, beaks, and claws of birds, and the scales and claws of reptiles. Keratin is a tough and insoluble protein that provides strength and protection to these structures.