hexagram

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A six-pointed star formed by extending each of the sides of a regular hexagon into equilateral triangles.
• noun A figure of six lines or sides.

from The Century Dictionary.

• noun A figure formed of two equilateral triangles placed concentrically with their sides parallel and on opposite sides of the center. This was the seal or symbol of the Pythagorean school.
• noun In geometry, a figure of six lines.
• noun In Chinese lit, one of the 64 figures which form the basis of the Yihking or “book of changes,” one of the oldest Chinese books. Each of these figures is made up of six parallel lines, of which some are whole and some divided. See book of changes, under change.

from the GNU version of the Collaborative International Dictionary of English.

• noun A figure composed of two equal triangles intersecting so that each side of one triangle is parallel to a side of the other, and the six points coincide with those of a hexagon.
• noun In Chinese literature, one of the sixty-four figures formed of six parallel lines (continuous or broken), forming the basis of the I Ching (Yih King), or “Book of Changes.”

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A hollow six-pointed star formed by overlapping two equilateral triangles; the Star of David.
• noun Any of the 64 sets of solid and broken lines used for divination in the I Ching.
• noun A large silver coin minted during the Byzantine Empire.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a regular polygon formed by extending each of the sides of a regular hexagon to form two equilateral triangles