once in a blue moon
Meaning
Very rarely; almost never; something that happens only on exceptional occasions.
Origin
From the notion of a “blue moon” as an extremely rare event; later tied to an occasional extra full moon in a season, reinforcing the idea of rarity.
Notes
Common, slightly informal phrase meaning “very rarely,” often with mild exaggeration or surprise. Fine in conversation; in formal writing, “rarely” or “seldom” may fit better.
Examples
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I go hiking once in a blue moon, but I wish I had more time for it.
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She only eats fast food once in a blue moon.
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We see our old neighbors once in a blue moon, usually around the holidays.
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Once in a blue moon, the train arrives early and everyone looks surprised.
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He calls his parents once in a blue moon, so they’re always happy to hear from him.
Grammar & Usage Notes
Typically used as an adverbial phrase: “once in a blue moon, …” or “I see him once in a blue moon.” Fixed wording; plural/tense changes are uncommon.
Synonyms
- rarely
- seldom
- hardly ever
- infrequently
- once in a while
Antonyms
- often
- frequently
- regularly
- all the time