Heptad
Heptad , noun
[Latin heptas the number seven. Greek {not transcribed}, {not transcribed}, from "epta` seven.]
(Chemistry) 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.