Hex"ad (?), n. [L. hexas, hexadis, the number six, Gr. , , fr. six.] chem.
An atom whose valence is six, and which can be theoretically combined with, substituted for, or replaced by, six monad atoms or radicals; as, sulphur is a hexad in sulphuric acid. Also used as an adjective.
© Webster 1913.