The Collaborative International Dictionary of English v.0.48:

Vanadium \Va*na"di*um\, n. [NL., fr. Icel. Vanad[imac]s, a
   surname of the Scandinavian goddess Freya.] (Chem.)
   A rare element of the nitrogen-phosphorus group, found
   combined, in vanadates, in certain minerals, and reduced as
   an infusible, grayish-white metallic powder. It is
   intermediate between the metals and the non-metals, having
   both basic and acid properties. Symbol V (or Vd, rarely).
   Atomic weight 50.94 (C12=12.000).
   [1913 Webster +PJC]

WordNet (r) 3.0 (2006):

vanadium
    n 1: a soft silvery white toxic metallic element used in steel
         alloys; it occurs in several complex minerals including
         carnotite and vanadinite [syn: vanadium, V, atomic
         number 23]