The Collaborative International Dictionary
Heptavalent
Heptavalent \Hep*tav"a*lent\, a. [Hepta- + L. valens, p. pr. See Valence.] (Chem.) Having seven units of attractive force or affinity; -- said of heptad elements or radicals.
Wiktionary
heptavalent
a. (context chemistry English) Having a valency of seven