blue moon
noun
1
: a very long period of time
—usually used in the phrase once in a blue moon
Such people happen along only once in a blue moon.—
Saturday Rev.
Saturday Rev.2
: a second full moon in a calendar month
Examples of blue moon in a Sentence
once in a blue moon we'll get dressed up and eat in a fancy restaurant
Recent Examples on the Web
The third full moon in a single season with four full moons is also sometimes referred to as a blue moon, though the actual color of the lunar disk remains normal for both definitions!
—Anthony Wood, Space.com, 1 May 2026
The second full moon on May 31 is a blue moon and will also be a micromoon, appearing smaller than usual.
—Mariyam Muhammad, USA Today, 30 Apr. 2026
This month’s blue moon is also a micromoon.
—Tom Hawking, Popular Science, 30 Apr. 2026
Under a blue moon, at 45 degrees below zero, on this night in 1999, the map of Canada split.
—Encyclopedia Britannica, 31 Mar. 2026
See All Example Sentences for blue moon
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Anthony Wood, Space.com, 1 May 2026
The second full moon on May 31 is a blue moon and will also be a micromoon, appearing smaller than usual.
—Mariyam Muhammad, USA Today, 30 Apr. 2026
This month’s blue moon is also a micromoon.
—Tom Hawking, Popular Science, 30 Apr. 2026
Under a blue moon, at 45 degrees below zero, on this night in 1999, the map of Canada split.
—Encyclopedia Britannica, 31 Mar. 2026
See All Example Sentences for blue moon
Cite this Entry
“Blue moon.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/blue%20moon. Accessed 4 May. 2026.
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