Hexad
Hexad , noun
[Latin hexas, hexadis, the number six, Greek {not transcribed}, {not transcribed}, from "e`x 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.