Enneagram (geometry)

In geometry, an enneagram (🟙 U+1F7D9) is a nine-pointed plane figure. It is sometimes called a nonagram, nonangle, or enneagon.

The word 'enneagram' combines the numeral prefix ennea- with the Greek suffix -gram. The gram suffix derives from γραμμῆ (grammē) meaning a line.

Regular enneagram
A regular enneagram is a 9-sided star polygon. It is constructed using the same points as the regular enneagon, but the points are connected in fixed steps. Two forms of regular enneagram exist:
 * One form connects every second point and is represented by the Schläfli symbol {9/2}.
 * The other form connects every fourth point and is represented by the Schläfli symbol {9/4}.

There is also a star figure, {9/3} or 3{3}, made from the regular enneagon points but connected as a compound of three equilateral triangles. (If the triangles are alternately interlaced, this results in a Brunnian link.) This star figure is sometimes known as the star of Goliath, after {6/2} or 2{3}, the star of David.

Other enneagram figures
The nine-pointed star or enneagram can also symbolize the nine gifts or fruits of the Holy Spirit.

In popular culture

 * The heavy metal band Slipknot previously used the {9/3} star figure enneagram and currently uses the {9/4} polygon as a symbol. The prior figure can be seen on the cover of All Hope Is Gone.