1. Idioms: Once in a blue moon
Nada Faleman - Structure

2. Nada Faleman - Structure 2- 1436 1437
Once in a blue moon:
Meaning: very rarely.
This expression is informal.
Use: although the appearance of a second full moon in the same calendar month-occurs every 32 months or so, speakers use the idiom to mean “rarely”.
Nada Faleman - Structure

3. Nada Faleman - Structure 2- 1436 1437
Examples:
My sister lives in Alaska, so I only get to see her once in a blue moon.
 Sarah: Does your husband ever bring 
you flowers? Hessah: Once in a blue moon. 
Once in a blue moon, I buy a fashion 
magazine, just to see what people are 
wearing.
Nada Faleman - Structure