adv.千载难逢地; 俟河之清; 百年不遇

千载难逢；极为罕见

blue moon once in a blue moon───蓝色月亮偶尔有一次

one in a million───百里挑一；极稀有的人或事

man in the moon───月球上的人

once in a while───偶尔；有时（等于everyonceinawhile）

once again once more───再一次

Such a chance comes once in a blue moon.───这样的机会极其难得.

It was an opportunity that comes once in a blue moon.───这种机会来一次可太难了.

It'snows here once in a blue moon.───这里几乎不下雪.

How often do you drink beer? B: Eh... once in a blue moon!───你多久喝一次啤酒？ B：呃……我难得喝一次！

Great writers like Mark Twain only appear once in a blue moon.───(像马克吐温那样伟大的作家,是很罕见的. )

He gets drunk only once in a blue moon.───他难得喝醉酒.

This is a chance once in a blue moon.───这可是个难得的机会.

Eg . Seeing the partial eclipse is once in a blue moon.───看见月偏食真是个千载难逢的事.

You get a chance like this only once in a blue moon.───这种机会你是很难得到的.

He gives us a treat only once in a blue moon.───他招待我们一顿可真是千载难逢.

That sort of thing only happens once in a blue moon.───这种事情难得发生一次.

He only comes here once in a blue moon.───他只是偶尔到这儿来一次.

Once in a blue moon you get some problems.───偶尔你也碰到一些麻烦.

Barry only visits his parents once in a blue moon.───巴里很难得去看望他父母一次.

Once in a blue moon is an informal phrase.───千载难逢） 是一个非正式短语。

This draught occurs once in a blue moon.───这场旱灾是百年不遇的.

I go to a restaurant once in a blue moon.───我难得在外吃饭,也极少在饭店用膳.