pentad
Pronunciation:
/ˈpɛntæd/noun
Definitions
A group or series of five things.
A mean average value of temperature, etc., taken every five days.
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.
Example: Nitrogen is a pentad in the ammonium compounds.