blue moon


: 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 moonSaturday Rev.
: 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 There will be a blue moon on Monday, Aug. 19, 2024. The Arizona Republic, 23 Feb. 2024 Then, to cap off the month, a full blue moon will be visible Aug. 30. Adithi Ramakrishnan, Dallas News, 1 Aug. 2023 Astronomy fans only get to see blue moons about once every three years on average. Christopher Brito, CBS News, 9 Aug. 2023 Skywatchers will be treated to a dozen full moons in 2024, as well as a seasonal blue moon in August. John Tufts, The Indianapolis Star, 2 Jan. 2024 August's super blue moon was the biggest of the year. Aliza Chasan, CBS News, 27 Sep. 2023 Idalia live updates: Forecast shows hurricane will be 'extremely dangerous' A blue moon refers to the second time a full moon appears during the same month, according to NASA. Teddy Grant, ABC News, 30 Aug. 2023 Regular blue moons and supermoons happen regularly. oregonlive, 30 Aug. 2023 It's been two years since the last blue moon is August 2021. Drew Dawson, Journal Sentinel, 28 Aug. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'blue moon.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History

First Known Use

1821, in the meaning defined at sense 1

Time Traveler
The first known use of blue moon was in 1821

Dictionary Entries Near blue moon

Cite this Entry

“Blue moon.” Dictionary, Merriam-Webster, Accessed 4 Mar. 2024.

Last Updated: - Updated example sentences
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!