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blue moon

[ bloo-moon ]
/ ˈblu ˈmun /
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idiom
a very long period of time: Such a chance comes once in a blue moon.
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Origin of blue moon

First recorded in 1815–25
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use blue moon in a sentence

British Dictionary definitions for blue moon

blue moon

noun
the second full moon occurring within a calendar month
once in a blue moon informal very rarely; almost never
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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