The Collaborative International Dictionary of English v.0.48:

Octavalent \Oc*tav"a*lent\, a. [Octa- + L. valens, p. pr. See
   Valence.] (Chem.)
   Having a valence of eight; capable of being combined with,
   exchanged for, or compared with, eight atoms of hydrogen; --
   said of certain atoms or radicals.
   [1913 Webster]