- any of the several fat-soluble, antirachitic vitamins D1, D2, D3, occurring in milk and fish-liver oils, especially cod and halibut, or obtained by irradiating provitamin D with ultraviolet light, essential for the formation of normal bones and teeth.
- any of the fat-soluble vitamins, including calciferol and cholecalciferol, occurring in fish-liver oils (esp cod-liver oil), milk, butter, and eggs: used in the treatment of rickets and osteomalacia
