vanadious

from The Century Dictionary.

• More specifically, containing vanadium as a constituent with apparently triad valence: as, vanadious oxid, V₂O₃. Vanadious salts in solution have a green color; they have not been much examined. Also vanadous.
• Containing vanadium with a lower apparent valence than it exhibits in vanadic compounds.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Chem.) Pertaining to, or containing, vanadium; specifically, designating those compounds in which vanadium has a lower valence as contrasted with the vanadic compounds. Usually written vanadous.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective vanadous