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
But a blue moon isn’t supposed to last for a year.
—Brett Owens, Forbes.com, 1 Sep. 2025
Black moons are referenced like blue moons, which are defined as the third full moon in an astronomical season containing four full moons.
—Janet Loehrke, USA Today, 21 Aug. 2025
The August 2025 full moon is not a rare super blue moon.
—Tiffany Acosta, AZCentral.com, 2 Aug. 2025
This spectacle will have a window of ideal visibility through February 21.
March 14: Total lunar eclipse
Sometimes, full moons get called colorful names that are a bit of a fake-out: A blue moon isn’t really blue, and a pink moon isn’t really pink.
—Carlyn Kranking, Smithsonian Magazine, 30 Dec. 2024
See All Example Sentences for blue moon
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Brett Owens, Forbes.com, 1 Sep. 2025
Black moons are referenced like blue moons, which are defined as the third full moon in an astronomical season containing four full moons.
—Janet Loehrke, USA Today, 21 Aug. 2025
The August 2025 full moon is not a rare super blue moon.
—Tiffany Acosta, AZCentral.com, 2 Aug. 2025
This spectacle will have a window of ideal visibility through February 21.
March 14: Total lunar eclipse
Sometimes, full moons get called colorful names that are a bit of a fake-out: A blue moon isn’t really blue, and a pink moon isn’t really pink.
—Carlyn Kranking, Smithsonian Magazine, 30 Dec. 2024
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 9 Sep. 2025.
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