Vanadious
Va`na´di`ous
| a. | 1. | (Chem.) Pertaining to, or containing, vanadium; specifically, designating those compounds in which vanadium has a lower valence as contrasted with the vanadic compounds; as, vanadious acid. Usually written vanadous. |
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.