D defs.my
Entry 1 sense Webster, 1913

Heptad

· Hep·tad · IPA /ˈhɛptæd/
01 n. An atom which has a valence of seven, and which can be theoretically combined with, substituted for, or replaced by, seven monad atoms or r…
  1. 1.
    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.(Chem.)