blue moon

noun

1

: a very long period of time

—usually used in the phrase once in a blue moon

such people happen along only once in a blue moon

—Saturday Rev.

2

: a second full moon in a calendar month

Synonyms

• aeon
• eon
• age
• coon's age
• cycle
• donkey's years [chiefly British]
• eternity
• forever
• long
• months
• moon

Examples of blue moon in a Sentence

once in a blue moon we'll get dressed up and eat in a fancy restaurant

Recent Examples on the Web

The last seasonal blue moon was in August 2021, and the next one won't occur until May 2027. —Tiffany Acosta, The Arizona Republic, 16 Aug. 2024

The second definition − which arose from a misunderstanding of the original − is the monthly blue moon, referring to the second full moon in a single calendar month. —Marley Malenfant, Austin American-Statesman, 16 Aug. 2024

As with supermoons, there are varying definitions for blue moons — monthly and seasonal. —Riane Lumer, CNN, 19 Aug. 2024

The Oilers were caught unaware because offer sheets are rare, and dual offer sheets happen just once in a very blue moon. —Allan Mitchell, The Athletic, 14 Aug. 2024

Word History

First Known Use

1821, in the meaning defined at sense 1