Word Study
heptad
CIDE DICTIONARY
heptad, n. [L. heptas the number seven. Gr. , , fr. "epta` seven.].
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. [1913 Webster]
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