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