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Idiom

once in a blue moon

idiom (adverbial phrase) B2
/wʌns ɪn ə bluː muːn/

Meanings

idiom (adverbial phrase)

Very rarely; almost never.

Visual cue for once in a blue moon — meaning 1

Definition

If something happens once in a blue moon, it happens very rarely.

“Once in a blue moon” means very infrequently, almost never. People use it to emphasize that an event does not happen often. It is common in casual speech when talking about habits, visits, or unusual situations.

Examples

  • I eat fast food once in a blue moon.
  • We see our cousins once in a blue moon because they live overseas.
  • She goes to the movies once in a blue moon now that she has a baby.
  • Once in a blue moon, the power goes out during a storm.