once in a blue moon
/wʌns ɪn ə blu mun/Very rarely; almost never
She visits her hometown once in a blue moon.
She visits her hometown very infrequently.
Blue moons are rare, so the phrase emphasizes how seldom something happens.
The idiom uses the rarity of a blue moon to describe infrequent events.
A 'blue moon' is an extra full moon that occurs about every 2.7 years, making the phrase emphasize extreme rarity.
Antonyms
Related Phrases
💡Pro Tip
Usage Tip
Use this phrase to describe events or actions that happen very infrequently, such as special occasions or rare habits.
⚡Gold Rule
Avoid Overuse
This phrase is best used for truly rare events. Overusing it can dilute its impact.
📖Word Origin
The phrase originates from the astronomical phenomenon of a blue moon, which is an extra full moon occurring about every 2.7 years. The rarity of this event led to its use as an idiom for something that happens very infrequently.
📝Usage Notes
This idiom is commonly used in informal contexts to emphasize how seldom something occurs. It is not used in formal or technical writing.