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

There's also a lot of supermoons in 2024 — four in a row, in fact, which began in August with a rare seasonal blue moon. —John Tufts, The Courier-Journal, 4 Sep. 2024

On Monday, a super blue moon lit up the night sky, giving people a glimpse at this rare spectacle. —Marley Malenfant, Austin American-Statesman, 20 Aug. 2024

Their version of Superman was made with blue moon, red pop and lemon flavors. —Jalen Williams, Detroit Free Press, 22 Dec. 2024

August is for Astronomy lovers:A rare, seasonal blue moon is coming, and the sky in August has more surprises in store John Tufts covers trending news for IndyStar and Midwest Connect. —John Tufts, The Indianapolis Star, 8 Aug. 2024

Word History

First Known Use

1821, in the meaning defined at sense 1