'Pentad' definitions:

Definition of 'pentad'

From: WordNet
noun
The cardinal number that is the sum of four and one [syn: five, 5, V, cinque, quint, quintet, fivesome, quintuplet, pentad, fin, Phoebe, Little Phoebe]

Definition of 'Pentad'

From: GCIDE
  • Pentad \Pen"tad\, n. [Gr. penta`s penta`dos, a body of five, fr. pe`nte five.] (Chem.) 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. [1913 Webster]
  • 2. Any grouping of five things. [PJC]

Definition of 'Pentad'

From: GCIDE
  • Pentad \Pen"tad\, a. (Chem.) Having the valence of a pentad. [1913 Webster] Pentadactyl