The Collaborative International Dictionary of English v.0.48:

vitamin C \vitamin C\ n.
   a vitamin that prevents scurvy. Also called ascorbic acid.

   Syn: ascorbic acid.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

ascorbic acid
    n 1: a vitamin found in fresh fruits (especially citrus fruits)
         and vegetables; prevents scurvy [syn: vitamin C, C,
         ascorbic acid]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "ascorbic acid":
   adermin, aneurin, antiberi-beri factor, axerophthol, biotin,
   carotene, cholecalciferol, choline, cobalamin, cryptoxanthin,
   cyanocobalamin, ergocalciferol, folic acid, hepatoflavin, inositol,
   lactoflavin, menadione, naphthoquinone, niacin, nicotinic acid,
   ovoflavin, pyridoxine, tocopherol, vitamin, vitamin B, vitamin Bc,
   vitamin D, vitamin G, vitamin H, vitamin K, vitamin M