once in a blue moon

[ wuhns in uh bloo moon ]

idiom

1. blue moon ( def 5 ).

once in a blue moon

1. To do something “once in a blue moon” is to do it very rarely: “That company puts on a good performance only once in a blue moon.” The phrase refers to the appearance of a second full moon within a calendar month, which actually happens about every thirty-two months.

Word History and Origins

Origin of once in a blue moon¹

First recorded in 1830–40

Idioms and Phrases

Rarely, once in a very long time, as in We only see our daughter once in a blue moon . This term is something of a misnomer, because an actual blue moon—that is, the appearance of a second full moon in the same calendar month—occurs every 32 months or so. Further, the moon can appear blue in color at any time, depending on weather conditions. [Early 1800s]

Example Sentences

Every once in a blue moon, our youngest daughter Amma has a Sunday soccer game; in that case, you’ll find me on the sidelines at her game.

From Los Angeles Times

It's a phenomenon - or, to use Chappell's terminology, a Femininomenon - that only occurs once in a blue moon.

From BBC

As blue moons are not that common, it's thought where the phrase "once in a blue moon" comes from.

From BBC

Kovacic's 64th-minute strike against Luton was one of those goals you see a defensive midfield player score once in a blue moon - no pun intended.

From BBC

If it were not for the undemocratic and unfair electoral college, we could all go to sleep since Trump will lose decisively in the popular vote once again as he and the Republican candidates always do except for "once in a blue moon."

From Salon

Related Words

• every now and then
• every so often
• infrequently
• intermittently
• now and again
• occasionally
• periodically
• sporadically