a blue moon

1. By living a blue moon with the Indians,he was assimilated to them in his thinking and actions.
由于长期和印第安人共同生活,他在思想和行动上都被他们同化了。

来自《简明英汉词典》

2. The story is just a blue moon.
这个故事根本就是件不可能的事。

来自《简明英汉词典》

3. Where have you been?I haven't seen you in a blue moon.
你到哪儿去了?我好久没见到你了。

来自《简明英汉词典》