Even if you only use idioms once in a blue moon, you have to download this one!
To do something “once in a blue moon” is to do it very rarely: “That company puts on a good performance only once in a blue moon.” The phrase refers to the appearance of a second full moon within a calendar month, which actually happens about every thirty-two months.
Synonyms: hardly ever, almost never, scarcely ever, rarely, very seldom
