Hep·tad n. Chem. 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.
n : the cardinal number that is the sum of six and one [syn: seven,
7, VII, sevener, septet]