Heptad
Pronunciation : Hep"tad
Part of Speech : n.
Etymology : [L. heptas the number seven. Gr. "epta` seven.] (Chem.)
Definition : Defn: An atom which has a valence of seven, and which can be theoretically combined with, substituted for, or replaced by, seven monad atoms or radicals; as, iodine is a heptad in iodic acid. Also used as an adjective.
Source : Webster's Unabridged Dictionary, 1913