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Webster 1913 Edition
Heptad
Hep′tad
,Noun.
[L.
heptas
the number seven. Gr. [GREEK], [GREEK], fr. ἑπτά
seven.] (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
. Also used as an adjective. heptad
in iodic acid