Definition of "pentad"

Synonym of quintet: A group of five things, particularly

1. Synonym of quinquennium: a five-year period, especially in reference to the first and second halves of calendrical decades.  examples

2. (climatology) A five-day period, especially a temperature average taken every five days.

3. A five-day division of the Chinese calendar, forming part of a solar term (Chinese: 候).  examples

4. (chemistry) A pentavalent element or group: an atom or molecule with a valence of five, comparable with five atoms of hydrogen.  examples