# once in a blue moon

> English word · Adverb · IPA /wʌns ɪn ə bluː muːn/

## Definitions
1. Very rarely; very infrequently.

## Etymology
See blue moon. First use appears c. 1833. See citation below.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-09-03.
Canonical page: https://plainspell.com/en/word/once-in-a-blue-moon