blue moon

noun

Definition of blue moon

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.

2 : a second full moon in a calendar month

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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 that happens twice in one month, the second event, like Wednesday’s, is traditionally called a blue moon. — Bruce Selcraig, San Antonio Express-News, "Supermoon, blood moon, blue moon — all coming Wednesday," 29 Jan. 2018 And the next blue moon won't come around until October 2020, according to the National Weather Service. — Leigh Morgan, AL.com, "Blue moon 2018: Second -- and last -- blue moon of year rises tonight," 1 Dec. 2017 The blue moon eclipse will occur on Wednesday, Jan. 31. — Aric Jenkins, Time, "Here's How to Watch the 'Super Blue Blood Moon Eclipse' Next Week," 24 Jan. 2018 The next blue moon — the second full moon in a calendar month — is only two months away, on March 31. — Doyle Rice, USA TODAY, "Missed the super blue blood moon eclipse? Here's when you'll see the next one.," 31 Jan. 2018 The total eclipse lines up with a supermoon, when the moon is biggest in the sky, as well as a blue moon, the second full moon in a calendar month. — Jay Bennett, Popular Mechanics, "NASA to Livestream Super Blue Blood Moon Through Telescopes Around the Country," 29 Jan. 2018 The full moon—in fact a supermoon and a blue moon—passed into Earth’s shadow or umbra, blocking the sun’s light, and making the surface of the moon appear a blood-red hue. — Sarah Gray, Fortune, "See Stunning Photos of the Super Blue Blood Moon Lunar Eclipse," 31 Jan. 2018 Kaibab Bob injured himself stumbling off the trail – as pack mules will, every once in a blue moon. — Stina Sieg, azcentral, "Stubbornly steadfast, pack mules keep Grand Canyon moving," 9 June 2018 Despite the annual-seeming moniker, this happens once in a blue moon. — Rachel Nussbaum, Glamour, "Tatcha Is Having a Ridiculously Good Sale Right Now," 3 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'blue moon.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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Last Updated

7 Oct 2018

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The first known use of blue moon was in 1821

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