Vitamin D Definition

Any of several fat-soluble vitamins that are essential for increased absorption of calcium and phosphorus from the intestinal tract, found in fish-liver oils, milk, egg yolk, etc. or produced by irradiation of provitamins.
Webster's New World
A white crystalline compound, C28 H44 O, produced by ultraviolet irradiation of ergosterol.
American Heritage
A colorless crystalline compound, C27 H44 O, found in fish-liver oils, irradiated milk, and all irradiated animal foodstuffs. It has essentially the same biological activity as vitamin D2 .
American Heritage