ennead

Since ancient times, various groups of people have considered nine to be a very special and sacred number. Legends and literature have long characterized groups of nine as having a special, in some cases magical, significance. Ancient Egyptians organized their gods into groups of nine; even today, their principal group of gods (headed by sun god Re-Atum) is called the "Great Ennead of Heliopolis." The Ennead English speakers use in that name traces to ennea, the Greek word for "nine." Ennead is also used generally to refer to other groups of ancient gods. Furthermore, it is the name given to six sets of nine treatises by Greek philosopher Plotinus that were collected and organized by his 3rd-century disciple, Porphyry.