once in a blue moon

Meaning

This expression means that something happens very rarely or almost never. It refers to the astronomical phenomenon of a second full moon in a single calendar month, which is quite uncommon. It is used in casual conversations to describe infrequent habits, rare visits, or unusual occurrences.

Examples

• My brother lives abroad, so we only see each other once in a blue moon.

  My brother lives abroad, so we only see each other once in a blue moon.

• I don't really like fast food, but I'll have a burger once in a blue moon.

  I don't really like fast food, but I'll have a burger once in a blue moon.

• He usually hates dressing up, but he wears a suit once in a blue moon.

  He usually hates dressing up, but he wears a suit once in a blue moon.

• Once in a blue moon, we get a heavy snowstorm in this part of the country.

  Once in a blue moon, we get a heavy snowstorm in this part of the country.

• She rarely watches television, only turning it on once in a blue moon.

  She rarely watches television, only turning it on once in a blue moon.

Common Mistakes

• ✗ I go to the gym once in blue moon.

  ✓ I go to the gym once in a blue moon.

  The indefinite article 'a' is a mandatory part of this fixed idiom. Omitting it sounds unnatural.

• ✗ We meet once on a blue moon.

  ✓ We meet once in a blue moon.

  The correct preposition is 'in', not 'on' or 'at'.

Related Expressions

Practice

• I'm not a big drinker, but I'll have a glass of wine ___.

  💡 Something that happens very rarely.

  Show answer

  once in a blue moon

• He cleans his room only ___, so it's usually a mess.

  💡 Think of a rare lunar event.

  Show answer

  once in a blue moon