pentad

noun5

1. •
   A five-day period, especially a temperature average taken every five days.
2. •
   Synonym of quintet: A group of five things.
3. •
   A five-day division of the Chinese calendar, forming part of a solar term (Chinese: 候).
4. •
   A pentavalent element or group: an atom or molecule with a valence of five, comparable with five atoms of hydrogen.

   • Nitrogen is a pentad in the ammonium compounds.
5. •
   Synonym of quinquennium: a five-year period, especially in reference to the first and second halves of calendrical decades.