千載難逢

千载难逢
qiānzǎinánféng
  1. extremely rare (idiom)
  2. once in a blue moon

CEDICT

once in a blue moon; not occurring once in a thousand years

Wiktionary

千年也難遇上一次，形容機會極為難得。

重編國語辭典

機會極為難得

維基詞典

Entry Composition

1 千載 qiānzǎi
  1. (literary) millennium
  2. (literary, figuratively) a long time
  3. a long time
  4. millennium
2 難 nán
  1. difficult (to...)
  2. problem
  3. difficulty
  4. difficult
  5. not good
3 逢 féng
  1. to meet by chance
  2. to come across
  3. (of a calendar event) to come along
  4. (of an event) to fall on (a particular day)
  5. to fawn upon