hexad

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A group or series of six.

Century Dictionary and Cyclopedia

1. n. The sum of six units; the number six; also, a series of six numbers.
2. n. In chem., an element the atoms of which have six times the saturating power or equivalence of the hydrogen atom, as sulphur in certain conditions.
3. n. Also spelled hexade.
4. n. A hexagon.
5. Having a combining power equivalent to six times that of hydrogen. Same as hexavalent and sexivalent.

Wiktionary

1. n. A group of six.

GNU Webster's 1913

1. n. (chem.) An atom whose valence is six, and which can be theoretically combined with, substituted for, or replaced by, six monad atoms or radicals. Also used as an adjective.

WordNet 3.0

1. n. the cardinal number that is the sum of five and one