pentavalent

from WordNet (r) 3.0 (2006)

pentavalent
    adj 1: having a valence of five

from The Collaborative International Dictionary of English v.0.48

Pentavalent \Pen*tav"a*lent\, a. [Penta- + L. valens, p. pr. See
   {Valence}.] (Chem.)
   Having a valence of five; -- said of certain atoms and
   radicals.
   [1913 Webster]