once in a blue moon

US 
UK 
  • na.〈非正式〉难得;罕见;千载难逢
  • Web难得一次;极少;千载难逢地
na.
1.
〈非正式〉难得;罕见;千载难逢

Sample Sentence

Definition:
Category:AllAll,OralOral,WrittenWritten,TitleTitle,TechnicalTechnical
Source:AllAll,DictionaryDictionary,WebWeb
Difficulty:AllAll,EasyEasy,MiddleMiddle,HardHard