[n] the cardinal number that is the sum of five and one
\Hex"ad\, n. [L. hexas, hexadis, the number six, Gr. ?, ?, fr. "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.