phrase🎓 English idiom

once in a blue moon

very rarely

What it means

Very rarely; on the few occasions that something happens infrequently. It emphasises how seldom an event occurs without giving an exact frequency.

Examples

  • We only eat out once in a blue moon because money is tight.
  • He visits his hometown once in a blue moon these days.
  • Once in a blue moon, she treats herself to an expensive dinner.
  • Snow falls here only once in a blue moon, so children love it.

Where it comes from

A 'blue moon' refers to a rare extra full moon in a season or month; the phrase took on its 'very rarely' meaning in the 19th century, building on older uses of 'blue moon' for something absurd or improbable.

Related idioms

#when pigs fly#at the drop of a hat#out of the blue#a long shot

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