The Collaborative International Dictionary of English v.0.48:

vitamin D \vitamin D\ n.
   any of several chemically related fat-soluble vitamins that
   prevent rickets. It is found in fish-liver oils, egg yolks
   and milk. Component vitamin D2 is also called calciferol,
   and vitamin D3 is called cholecalciferol.

   Syn: calciferol, ergocalciferol, cholecalciferol.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

vitamin D
    n 1: a fat-soluble vitamin that prevents rickets [syn: vitamin
         D, calciferol, viosterol, ergocalciferol,
         cholecalciferol, D]