Definition of: casein

(kā′sē·in, -sēn) noun Biochem.
A phosphoprotein found especially in milk, constituting the principal ingredient in cheese: a white friable substance of acid character, used in preparing cotton cloth for calico printing, as an adhesive in certain varieties of cement, and as an important ingredient in plastics and synthetic resins. [<L caseus cheese]
—ca·se·ic (kā′sē·ik) adjective