asterism

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

• noun Printing Three asterisks in a triangular formation used to call attention to a following passage.
• noun Astronomy A pattern of stars that is not one of the traditionally established, named constellations, such as the Big Dipper or the Summer Triangle. Asterisms are often named and may be composed of stars that are members of one or more constellations.
• noun Mineralogy A six-rayed starlike figure optically produced in some crystal structures by reflected or transmitted light.

from The Century Dictionary.

• noun A group of stars: formerly equivalent to constellation, but now appropriated to any small cluster of stars, whether a part of a constellation or not.
• noun An asterisk, or mark of reference.
• noun Three asterisks placed thus, , or thus, , before a passage, to direct attention to it.
• noun An optical property exhibited by some crystallized minerals which show a star-shaped luminous figure when viewed by reflected light, as the asteriated sapphire, or by transmitted light, as some kinds of phlogopite.

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

• noun obsolete A constellation.
• noun A small cluster of stars.
• noun rare An asterisk, or mark of reference.
• noun Three asterisks placed in this manner, ⁂, to direct attention to a particular passage.
• noun (Crystallog.) An optical property of some crystals which exhibit a star-shaped by reflected light, as star sapphire, or by transmitted light, as some mica.

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

• noun astronomy A small group of stars that forms a visible pattern but is not an official constellation.
• noun A rarely used typographical symbol (⁂, three asterisks arranged in a triangle), used to call attention to a passage or to separate subchapters in a book.
• noun mineralogy A star-shaped figure exhibited by some crystals by reflected light (as in a star sapphire) or by transmitted light (as in some mica).

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

• noun (astronomy) a cluster of stars (or a small constellation)
• noun (mineralogy) a star-shaped figure with six rays that is seen in some crystal structures under reflected or transmitted light