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
When this happens, the second full moon is called a blue moon.
—Alexis Simmerman, Austin American Statesman, 29 Jan. 2026
Each type of blue moon happens roughly every 2-3 years.
—John Tufts, IndyStar, 7 Jan. 2026
The year 2026 will feature 13 full moons, including a rare monthly blue moon in May.
—Tiffany Acosta, AZCentral.com, 3 Jan. 2026
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
See All Example Sentences for blue moon
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Alexis Simmerman, Austin American Statesman, 29 Jan. 2026
Each type of blue moon happens roughly every 2-3 years.
—John Tufts, IndyStar, 7 Jan. 2026
The year 2026 will feature 13 full moons, including a rare monthly blue moon in May.
—Tiffany Acosta, AZCentral.com, 3 Jan. 2026
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
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 31 Jan. 2026.
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