Function: noun
Date: circa 1921
: any or all of several fat-soluble vitamins chemically related to steroids, essential for normal bone and tooth structure, and found especially in fish-liver oils, egg yolk, and milk or produced by activation (as by ultraviolet irradiation) of sterols: as a or vitamin D 2 \ - ' d ē - ' tü \ : CALCIFEROL b or vitamin D 3 \ - ' d ē - ' thr ē \ : CHOLECALCIFEROL