blue moon

[ bloo moon ]

noun

1. a second full moon in a month, occurring every two to three years as a result of the discrepancy between a lunar year and a solar year.
2. (formerly) the third full moon in a season with four full moons instead of the usual three.
3. a long, indeterminate stretch of time, as between occurrences of a rare event or phenomenon.
4. an uncommon phenomenon in which the moon appears to have a blue tinge because of the filtering effect of smoke or dust particles in the atmosphere.

idiom

1. a very long period of time:

   Such a chance comes once in a blue moon.

blue moon

noun

1. the second full moon occurring within a calendar month
2. once in a blue moon informal.
   very rarely; almost never

Word History and Origins

Origin of blue moon¹

First recorded in 1815–25

Example Sentences

I go back and forth between feeling like, “This is happening all around us,” versus, “This happens once in a blue moon.”

From Nautilus

A gorgeous, glistening rendition of “Lost Cause” came next, and the airy Morning Phase standout “Blue Moon” ended the sequence.

From The Daily Beast

Blue Moon has some really nice orange zest and coriander flavors that finish with a wonderful smoothness.

From The Daily Beast

The “dark” fruit that seemed to work best with Blue Moon was blueberries.

From The Daily Beast

He was the guy who came along once in a blue moon to save the country.

From The Daily Beast

As a brand, Blue Moon beer is not unlike Blue Dog Democrats, walking the tightrope of competing identities.

From The Daily Beast

But conductors are no more infallible than other people, and once in a blue moon in going through a train they miss a passenger.

From Project Gutenberg

"A purple sea, a blue moon, and a red fish—it looks crazy to me," muttered the old agent.

From Project Gutenberg

He was seated beside the great, wood-burning stove in the great front room of the Blue Moon.

From Project Gutenberg

When they gathered in the back room of the Blue Moon, the players found a blackboard hung upon the wall.

From Project Gutenberg

And a mighty horde in trucks, busses, and private cars, some even on bicycles was pouring toward the Blue Moon at sunset.

From Project Gutenberg