blue moon


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 moonSaturday Rev.

2 : a second full moon in a calendar month

Keep scrolling for more

Synonyms for blue moon


aeon (or eon), age, coon's age, cycle, donkey's years [chiefly British], eternity, forever, long, months, moon

Visit the Thesaurus for More 

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

Barring clouds in the northwest sky, Wednesday's total eclipse of the blue moon will be visible low in the western sky. Mike De Sisti, Milwaukee Journal Sentinel, "How to photograph, make the super-blood-blue-moon total eclipse a family event," 30 Jan. 2018 The colorful new addition—a white unicorn with purple and blue highlights—will join the current mainstays: heart, star, horseshoe clover, blue moon and red balloon marshmallows—and replace the hourglass, which was retired earlier this month. Collier Sutter,, "Lucky Charms Debuts a New Marshmallow for the First Time in a Decade," 20 Feb. 2018 The rare blue blood moon was combination of a supermoon, blue moon and total lunar eclipse. Ashley May, USA TODAY, "Incredible images of the rare blue blood moon," 31 Jan. 2018 Can one full moon be a blue moon, a blood moon and a supermoon all at once? Joe Marusak, charlotteobserver, "Here’s how to watch the ‘super blue blood moon’ early Wednesday," 29 Jan. 2018 Lunar eclipses occur up to three times a year, supermoons about once every 14 months, and blue moons about once every 2.7 years, according to David Freeman /, NBC News, "A 'super blue blood moon' is coming. Here's how to see it," 24 Jan. 2018 This year there were two blue moons — January and March each had two moons, an anomaly that's fairly rare. Meg Jones, Milwaukee Journal Sentinel, "Look up! Strawberry Moon is most colorful full moon all year," 25 June 2018 February didn’t get a full moon, as January scored a full moon and a blue moon. Blaine P. Friedlander Jr., Washington Post, "Skywatch: In March, planets loiter together in the evening and morning heavens," 24 Feb. 2018 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

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.

See More

First Known Use of blue moon

1821, in the meaning defined at sense 1

Keep scrolling for more

Learn More about blue moon

Statistics for blue moon

Last Updated

2 Dec 2018

Look-up Popularity

Time Traveler for blue moon

The first known use of blue moon was in 1821

See more words from the same year

More from Merriam-Webster on blue moon

Rhyming Dictionary: Words that rhyme with blue moon

Thesaurus: All synonyms and antonyms for blue moon

Comments on blue moon

What made you want to look up blue moon? Please tell us where you read or heard it (including the quote, if possible).


the figure or shape of a crescent moon

Get Word of the Day daily email!

Test Your Vocabulary

Late Autumn 2018 Words of the Day Quiz

  • frosted-autumn-leaves
  • Which is a synonym of yahoo?
Spell It

Can you spell these 10 commonly misspelled words?

Add Diction

Test Your Knowledge - and learn some interesting things along the way.


Love words? Need even more definitions?

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