The Collaborative International Dictionary of English v.0.48:

Vanadic \Va*nad"ic\, a. (Chem.)
   Pertaining to, or obtained from, vanadium; containing
   vanadium; specifically, designating those compounds in which
   vanadium has a relatively higher valence as contrasted with
   the vanadous compounds; as, vanadic oxide.
   [1913 Webster]

   Vanadic acid (Chem.), an acid analogous to phosphoric acid,
      not known in the free state but forming a well-known
      series of salts.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vanadic acid
    n 1: any of various oxyacids of vanadium; known mostly in the
         form of its salts [syn: vanadium pentoxide, vanadic
         acid]