Once in a Blue Moon – Idiom, Meaning & Origin

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Candace Osmond

Candace Osmond studied Advanced Writing & Editing Essentials at MHC. She’s been an International and USA TODAY Bestselling Author for over a decade. And she’s worked as an Editor for several mid-sized publications. Candace has a keen eye for content editing and a high degree of expertise in Fiction.

In the twinkling cosmos of idioms and phrases, few expressions can match the poetic allure of the phrase once in a blue moon. It makes you think of a night sky painted with mystic hues, doesn’t it? Well, let’s unpack this enchanting phrase and learn the meaning of once in a blue moon.

Understanding the Meaning of Once in a Blue Moon

Once in a Blue Moon Idiom Meaning Origin

When we say something happens once in a blue moon, we don’t mean it occurs every time the moon takes on a blueish tint. The phrase is actually used to pinpoint an event that happens very rarely.

Tracing Back the Origin and Etymology of the Phrase

Let’s take a look at the history of this idiomatic expression. Contrary to what you might expect, the term blue moon doesn’t come from a moon that’s suddenly decided to change its color palette. The phrase goes back to 16th-century England when it was used to describe absurdities. After all, moons turning blue seemed as absurd as pigs flying!

Over the centuries, the meaning evolved. By the 19th century, blue moon was used in the Maine Farmers’ Almanac to refer to the rare occurrence of four full moons within a season (which typically has three). The third full moon of a season was coined a blue moon.

But the saying is also tied to the fact that actual blue moons exist. It’s from a combination of random atmospheric events that give the moon a blue tinge. A real moon that’s blue is also extremely rare, so it’s connected to the phrase.

Once Every Blue Moon or Once in a Blue Moon?

Once In a Blue Moon vs Once Every Blue Moon Ngram
Once in a blue moon and once every blue moon usage trend.

Now, if you’re scratching your head over whether to say once every blue moon or once in a blue moon, let me ease your confusion. Both phrases mean the same thing and are both correct, but once in a blue moon is more widely accepted and used.

Synonyms for Once in a Blue Moon

If you’re keen on jazzing up your conversation with synonyms, here’s a list I whipped up!

  • Rarely
  • Hardly ever
  • Infrequently
  • On rare occasions
  • Once in a coon’s age (a very informal, mostly American phrase)

Using Once in a Blue Moon in Sentences

Once in a Blue Moon Idiom Meaning Origin 1

Now, let’s see how to sprinkle this phrase into your daily conversation with a few examples in sentences.

  • John visits his hometown once in a blue moon, making each trip a massive family reunion.
  • I indulge in a lavish, bookish shopping spree once in a blue moon and stock up on all my favorite books in hardcover.
  • My sister, a complete fitness enthusiast, only skips her workout once in a blue moon.
  • Once every blue moon, my kids are well-behaved enough to take in public.

Bidding Adieu Until the Next Blue Moon

With my tips and insights, you should be ready to use the phrase once in a blue moon wherever you like. Remember, idioms like these can add a touch of charm and whimsy to language if used correctly. So, don’t hesitate to use them, even if it’s just once in a blue moon!