once in a blue moon

American  

[wuhns in uh bloo moon] / ˈwʌns ɪn ə ˈblu ˈmun /

idiom

1. blue moon.

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once in a blue moon Cultural  

1. To do something “once in a blue moon” is to do it very rarely: “That company puts on a good performance only once in a blue moon.” The phrase refers to the appearance of a second full moon within a calendar month, which actually happens about every thirty-two months.

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once in a blue moon More Idioms  

1. Rarely, once in a very long time, as in We only see our daughter once in a blue moon. This term is something of a misnomer, because an actual blue moon—that is, the appearance of a second full moon in the same calendar month—occurs every 32 months or so. Further, the moon can appear blue in color at any time, depending on weather conditions. [Early 1800s]

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Etymology

Origin of once in a blue moon

First recorded in 1830–40

Example Sentences

Once in a blue moon, a person is willing to do the hard internal work that leads to real, sustainable change.

From Salon • Mar. 21, 2025

Once in a blue moon, the story of an ending was one of a happy retirement, of people and a place having created a lot of joy for a long time, plate after plate.

From Seattle Times • Jul. 16, 2020

Once in a blue moon, readers encounter a standout memoir that offers a glimpse into a life so vividly drawn that the story feels, impossibly, universal.

From Los Angeles Times • Dec. 20, 2019

Once in a blue moon I'll have a nice blow out on chocolate and it'll make me feel much better.

From The Guardian • Mar. 4, 2011

Once in a blue moon, I’ve seen my mother try something similar, but not often.

From "Catching Fire" by Suzanne Collins

Related Words

• every now and then
• every so often
• infrequently
• intermittently
• now and again
• occasionally
• periodically
• sporadically