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Once In a Blue Moon

A cloudy night sky with a blue tinted moon. once in a blue moon

Once In a Blue Moon Definition

Once In a blue moon.

  • Very rarely
  • On rare occasions


A blue moon refers to a second full moon in the same calender month. Something that actually only occurs roughly every thirty two months.

Once In a Blue Moon Examples

  • “Looks like your son really likes basketball” Jeff said looking out the window at the boy chasing after his ball. “Yup! He even gets it in the hoop, once in a blue moon. ” Daniel joked.
  • Once In a blue moon that songbird will land at my bird feeder, and every time he sings the most beautiful tune.


But once in a while the odd thing happens,

Once in a while the dream comes true,

And the whole pattern of life is altered,

Once in a while the moon turns blue.

W. H. Auden

Once in a blue moon someone like you comes along.

Van Morrison

Once In a Blue Moon Origin

Literary Origin

Yf they saye the mone is belewe,

We must beleve that it is true.

Treatyse of the Buryall of the Masse, William Barlow, 1528

The earliest our idiom appears in text is in the Treatyse of the Buryall of the Masse. This anti-clerical pamphlet was written in 1528 by William Barlow bishop of Chichester.

This passage uses the phrase more literally to say that a group of guillable or uneducated people would be compelled to believe whatever you tell them. Including that the moon is blue.

Spiritual Origin

Their attention was at this moment attracted by the appearance of two persons dressed in the extreme of fashion, who, upon meeting just by them, caught eagerly hold of each other’s hand, and they overheard the following—’Why, Bill, how am you, my hearty?—where have you been trotting your galloper?—what is you arter?—how’s Harry and Ben?—haven’t seen you this blue moon

Real Life In London, Pierce Egan, 1821

A similar phrase that first holds the meaning of our idiom appears in the serial journals the Real Life in London by the 19th century British sports writer Pierce Egan.

Real Life in London was a series of publications featuring fictitious characters Jerry Hawthorn and Corinthian Tom as they rambled and experienced the high and low life of the titular English city. The famous author William Makepeace Thackeray was quite a fan of Pierce’s works.

The journals also titled the Day and Night Scenes of Jerry Hawthorn, Esq., and his elegant friend, Corinthian Tom, inspired a series a plays based on them. These plays were simply titled Tom and Jerry. It is believed, but not proven, that the famous cat and mouse cartoon duo of Tom and Jerry got their names from adaptations of the characters in Egan’s plays.