PENTAD n.
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.
PENTAMEROUS a.
Divided into, or consisting of, five parts; also, arranged in sets, with five parts in each set, as a flower with five sepals, five petals, five, or twice five, stamens, and five pistils.