What does “Once in a blue moon” mean?
Something that happens very rarely or almost never.
Main example sentence
“Since moving abroad, he only visits his hometown once in a blue moon.”
How and when to use it
Use it for events that do happen, but with long or unpredictable gaps between them. It is common in everyday conversation and informal writing. The idiom usually functions as an adverbial phrase, telling the listener how often an action occurs.
More natural examples
- We eat at expensive restaurants only once in a blue moon.
- Once in a blue moon, the whole family manages to meet on the same weekend.
- She checks social media once in a blue moon now.
- A quiet morning like this comes along once in a blue moon.
How rare is it?
The phrase suggests much less often than occasionally. It is deliberately imprecise: the speaker emphasizes rarity rather than promising a measurable schedule.
Does the moon turn blue?
In ordinary use, the speaker is not describing the moon’s color. The phrase is understood as a figurative marker of rarity.
Where it fits in a sentence
It can appear at the beginning or end of a clause: 'Once in a blue moon, we travel together' and 'We travel together once in a blue moon' are both natural.