casein

ca·sein

noun \ˈkā-ˌsēn, ka-ˈsēn\

Definition of CASEIN

: any of several phosphoproteins of milk: as a : one that occurs as a colloidal suspension in milk—called also caseinogen b : one that is produced when milk is curdled by rennet, is the chief constituent of cheese, and is used in making plastics—called also paracasein