calciferol(n = noun.substance) cholecalciferol, d, ergocalciferol, viosterol, vitamin d - a fat-soluble vitamin that prevents rickets;
is a kind of fat-soluble vitamin

   one of the forms of vitamin D, a fat-soluble vitamin that prevents rickets. It is an unsaturated alcohol, C28H43OH found in foods such as milk and fish liver oils. It is used as a dietary supplement in milk. [WordNet 1.5]

calciferol, n. one of the D vitamins, routinely added to dairy products, essential for the deposition of calcium in bones. Also called ERGOCALCIFEROL, vitamin D2.

Etymology:
CALCIFEROUS + -OL(1)