hexad

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A group or series of six.

from The Century Dictionary.

• noun The sum of six units; the number six; also, a series of six numbers.
• noun 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.
• noun Also spelled hexade.
• noun A hexagon.
• Having a combining power equivalent to six times that of hydrogen. Same as hexavalent and sexivalent.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A group of six.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the cardinal number that is the sum of five and one