What is "the enneads"

Ennead \En"ne*ad\, n. [Gr. ?, ?, fr. 'enne`a nine.] The number nine or a group of nine.

The Enneads, the title given to the works of the philosopher Plotinus, published by his pupil Porphyry; -- so called because each of the six books into which it is divided contains nine chapters.