once in a blue moon

Meaning

Very rarely; almost never.

Examples

1. We eat at restaurants once in a blue moon, because cooking at home is cheaper. US UK
2. My brother lives abroad, so I see him once in a blue moon. US UK
3. She calls only once in a blue moon, usually on my birthday. US UK

How to use it

It usually goes at the end of the sentence. Compare the frequency: sometimes is more often, rarely is not often, and once in a blue moon is almost never.

Common mistake

Not: I go to the cinema in a blue moon.
Say: I go to the cinema once in a blue moon. (Keep the word “once”.)