Pentad /(?)/

Pen·tad

Pentad

n.
  1. Any element, atom, or radical, having a valence of five, or which can be combined with, substituted for, or compared with, five atoms of hydrogen or other monad; as, nitrogen is a pentad in the ammonium compounds. (Chem.)
  2. Any grouping of five things.

Pentad

a.
  1. Having the valence of a pentad. (Chem.)