in a blue moon

基本解釋

From this perspective, unused functions should not be dropped from software merely because they are used once in a blue moon.
從這個觀點(diǎn)來說，不習(xí)慣使用的功能不應(yīng)該僅僅從軟件中去除因爲(wèi)他們往往給使用他們的用戶一種千載難逢的感覺。
To keep the game interesting, most of it is paid out in dribs and drabs: a machine that returned $95,000 of every $100,000 in one huge jackpot once in a blue moon would be too disheartening to play.
爲(wèi)了讓賭戯保持吸引力，機(jī)器廻餽的獎金都是零零碎碎的：如果在一廻千載難逢的機(jī)遇下一次性返還獎池內(nèi)10萬美元的95%則太過令人沮喪，玩興全無。
In English we say “once in a blue moon”.
“千載難逢”用英語我們說“once in a blue moon” 。
edu.sina.com.cn

Occasionally it will be hundreds of millions and once in a blue moon billions.
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And then, every once in a blue moon, something comes along that is in a category all its own.
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Once in a blue moon, he tells me, he saw an iPhone.
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