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

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

Tuesday's supermoon will mark the second of four consecutive supermoons, the next being Thursday, Oct. 17: Aug. 19: super blue moon Sept. 17: supermoon, harvest moon and partial lunar eclipse Oct. 17: supermoon Nov. 15: supermoon More:Missed the rare super blue moon? —Alexis Simmerman, Austin American-Statesman, 16 Sep. 2024

This month’s rare super blue moon peaks at 11:25 a.m. —Kelsie Gibson, Peoplemag, 16 Aug. 2024

Word History

First Known Use

1821, in the meaning defined at sense 1