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
Typically, full moons happen every 29 days, while most months in our calendar last 30 or 31 days, so the months and moon phases don’t exactly align — resulting in a blue moon about every 2 ½ years.
—Ashley Strickland, CNN Money, 31 Dec. 2025
Super blue moons can also occur, but don’t be fooled by the name.
—Callum Sutherland, Time, 6 Oct. 2025
But sometimes, once in a magical blue moon, a star will stray from the norm—and pop up in the most random of places.
—Christian Allaire, Vogue, 18 Sep. 2025
But a blue moon isn’t supposed to last for a year.
—Brett Owens, Forbes.com, 1 Sep. 2025
See All Example Sentences for blue moon
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Ashley Strickland, CNN Money, 31 Dec. 2025
Super blue moons can also occur, but don’t be fooled by the name.
—Callum Sutherland, Time, 6 Oct. 2025
But sometimes, once in a magical blue moon, a star will stray from the norm—and pop up in the most random of places.
—Christian Allaire, Vogue, 18 Sep. 2025
But a blue moon isn’t supposed to last for a year.
—Brett Owens, Forbes.com, 1 Sep. 2025
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 Jan. 2026.
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