What is a group of eight called?

A group of eight can be called an octad (things) or an octet (often performers), or even an eightsome. A related adjective is octonary (related to or based on eight). In Egyptian Mythology there was a group of eight deities called the Ogdoad (the eightfold).

There are also groups that are comprised of eight that go by other things. The "Group of Eight" industrialized countries is known just like that, or by the abbreviation G8. There is also a group called the "Group of Eight" that are Australian Universities.