Once in a blue moon is a popular English idiom used to describe something that happens very rarely. In this article, IDP will explore the meaning, usage, and related expressions to help you master this idiom and apply it effectively in both IELTS Speaking and real-life conversations.
1. What Does “Once in a Blue Moon” Mean?
According to the Cambridge Dictionary, once in a blue moon means “not very often”. It is used to describe actions or events that rarely occur.
Meaning: Something that happens very infrequently
Examples:
My parents go on a vacation together once in a blue moon, so they’re really excited this time.
Lena cooks dinner once in a blue moon, so we know it’s a special occasion when she does.
2. Origin and Usage of “Once in a Blue Moon”
The idiom originates from a rare astronomical event where two full moons appear in the same calendar month—something that only happens every 2–3 years. Despite its name, the moon does not actually turn blue. Because of its rarity, this event inspired the idiom to describe things that happen very infrequently.
The phrase dates back to the 16th century in literature, originally referring to absurd or unbelievable things. Its modern meaning of “rarely” became more common in the 19th century.
How to Use “Once in a Blue Moon”
Function: Adverb of frequency (similar to “rarely” or “hardly ever”)
Placement: Beginning, middle, or end of a sentence
Examples:
Once in a blue moon, I treat myself to a spa day after a hectic week.
He calls his cousins once in a blue moon, even though they used to be close.
Do you go camping? Or is it just once in a blue moon?
Note: “Once in a blue moon” is a fixed phrase. Do not modify it or combine it with other frequency expressions.
3. Phrases Related to “Once in a Blue Moon”
Below are other English phrases that express rarity or infrequency, each with a slightly different tone or level of formality:
Phrase | Meaning | Example |
|---|---|---|
Rarely | Not often | I rarely watch horror movies because they keep me up at night. |
Seldom | Almost never | She seldom travels abroad due to work commitments. |
Hardly ever | Nearly never | He hardly ever checks his emails on weekends. |
Infrequently | Not often (formal) | This species of bird appears infrequently in the area. |
Once in a while | Occasionally | Once in a while, I enjoy watching old classic movies. |
From time to time | Occasionally | From time to time, I treat myself to a nice dinner. |
Every now and then | Occasionally | Every now and then, he surprises us with his cooking skills. |
On rare occasions | Rarely | On rare occasions, she’ll sing at family gatherings. |
Once in a great while | Extremely rarely | Once in a great while, we take a spontaneous road trip. |
Scarcely ever | Hardly ever | They scarcely ever take public transportation. |
Not often | Infrequent | He doesn’t go out for lunch, not often anyway |
4. Using “Once in a Blue Moon” in IELTS Speaking and Daily Conversation
In IELTS Speaking
Using idioms like “once in a blue moon” can impress the examiner and help you achieve a higher lexical resource score. It’s especially useful in Part 1 when talking about personal habits or routines.
Sample Question: Do you like eating out?
Sample Answer: Not very often, to be honest. I usually cook at home, but once in a blue moon, I enjoy going out for a fancy dinner with my friend.
In Real-life Conversation
Example Dialogue:
Anna: Have you been to the new art gallery downtown?
Ben: Not yet. I only visit art galleries once in a blue moon.
Anna: You should check it out. They have an exhibition I think you’d enjoy.
Ben: Sounds interesting. Maybe this will be the occasion that breaks my “once in a blue moon” habit.
5. Practice Exercises: “Once in a Blue Moon” (With Answers)
Exercise: Rewrite the following sentences using “once in a blue moon”
I almost never eat fast food because I prefer home-cooked meals. → ………………………………………………………………………
She seldom goes shopping because she saves most of her money. → ………………………………………………………………………
We hardly ever travel during the winter holidays. → ………………………………………………………………………
He doesn't usually forget people's names, but it does happen once or twice. → ………………………………………………………………………
I don’t often wake up late, unless I go to bed very late the night before. → ………………………………………………………………………
Suggested Answers:
I eat fast food once in a blue moon because I prefer home-cooked meals.
She goes shopping once in a blue moon because she prefers to save money.
We travel during the winter holidays once in a blue moon.
He only forgets people's names once in a blue moon.
I wake up late once in a blue moon, usually after staying up too late.
Master IELTS Speaking with “Once in a Blue Moon” and IDP
Incorporating idioms like once in a blue moon into your IELTS Speaking responses can make your answers more engaging and help boost your vocabulary score. It’s also a great way to sound more natural in everyday conversation.
With IDP’s high-quality preparation resources and expert support, you can confidently aim for your target score. Whether you're taking the IELTS Academic Speaking or IELTS General Speaking, IDP offers flexible test dates and conveniently located test centers across Vietnam.
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