Casein \Ca"se*in\, n. [Cf. F. cas['e]ine, fr. L. caseur cheese. Cf. Cheese.]

(Physiol. Chem.) A proteid substance present in both the animal and the vegetable kingdom. In the animal kingdom it is chiefly found in milk, and constitutes the main part of the curd separated by rennet; in the vegetable kingdom it is found more or less abundantly in the seeds of leguminous plants. Its reactions resemble those of alkali albumin. [Written also caseine.]

Source: Webster's Revised Unabridged Dictionary (1913)