Ennea

Ennea is a Greek root meaning nine. In English, it appears as a combining form in a variety of terms related to the number nine, and it is used to name objects, groups, or concepts that involve nine elements.

In geometry, ennea- forms several terms. A nine-sided polygon can be called an enneagon or, less commonly, a nonagon. A nine-faced polyhedron is termed an enneahedron. The more familiar prefix for many modern polygon names is non-, but enneagon and related forms are still encountered in mathematical and historical literature.

The term ennead designates a group of nine. In ancient Egyptian religion, the Ennead (or Great Ennead) refers to a grouping of nine deities worshipped together at Heliopolis, including Atum, Shu, Tefnut, Geb, Nut, Osiris, Isis, Seth, and Nephthys. The concept appears in other traditions and scholarly works as a generic label for any assembly of nine.

Enneagram refers to a nine-pointed figure or diagram used in various contexts, most prominently in a personality framework known as the Enneagram of Personality. The symbol consists of a circle with nine points connected by lines, and it is employed in spirituality, psychology, and self-study to map nine interrelated types.

In general usage, ennea serves as a linguistic tool to denote nine or ninefold structures across disciplines, from mathematics to theology and beyond.