qiān zǎi yī shí

a golden opportunity; an extremely rare chance (opportunity); a (very) rare opportunity; only once in a thousand years; (A thing like that) only happens once in a blue moon; a time of a thousand years; the chance of a lifetime:

【释义】一千年才有这么一个时机。形容机会极其难得。

【近义】千载难逢、百年不遇、铁树开花

【反义】习以为常、俯拾即是

【出处】晋·王羲之《与会稽王笺》：“遇千载一时之运，顾智力屈于当年。”

【用例】圣天子赫然有意千载一时之治，删弃文法，捐除科条，裁损吏议，亲总其大纲大纪，以进退一世。（清·龚自珍《明良论》）