blue moon

Noun

 * 1)  An extra full moon that appears in a subdivision of a year, namely:
 * 2) The third full moon in a season that contains four rather than the usual three full moons.
 * 3) The second of two full moons that occur in the same calendar month (a definition created by mistake in the 20th century).
 * 4)  The moon tinted towards blue as it appears in the sky, caused by dust or smoke in the atmosphere.
 * 5)  A long time.
 * 6)  A bright blue, sweet-flavored ice cream that is popular in the Midwestern U.S. and is a component of Superman ice cream.