blue moon definition by Webster's New World
Origin: ; from a rare atmospheric condition in which layers of smoke, dust, and the like , as from forest fires, volcanoes, and the like , cause the surface of the moon to appear to be blue
blue moon definition by American Heritage Dictionary
- a. The third full moon in a three-month calendrical season that has four full moons.b. The second of two full moons occurring in the same month.
- Informal A relatively long period of time: I haven't seen you in a blue moon.
Origin: Sense 2, probably from the rare occurrence whereby the moon appears blue from high amounts of dust in the atmosphere, as from a volcanic eruption.
blue moon - Phrases/Idioms
once in a blue moon