一诺千金

一諾千金
yīnuòqiānjīn
  1. lit. a promise worth a thousand pieces of gold (idiom)
  2. fig. a promise that can be counted on

CEDICT

to be true to one's word

Wiktionary

语本《史记．卷一○○．季布传》：「曹丘至，即揖季布曰：『楚人谚曰：「得黄金百，不如得季布一诺」，足下何以得此声于梁楚閒哉？』」形容承诺信用高，一旦许诺别人，必定做到。宋．杨万里〈答隆兴张尚书〉：「再有后日特剡之议，得玉求剑，敢萌此心，一诺千金，益深谢臆。」《金瓶梅．第五五回》：「因为那归的忙促，不曾叩府辞别。正在想着，不意一诺千金，远蒙员外记忆。」也作「千金一诺」。

重編國語辭典

形容承诺信用高，一旦许诺别人，必定做到

維基詞典

Entry Composition

1 一 yī
  1. one
  2. single
  3. a (article)
  4. as soon as
  5. entire; whole; all; throughout
  6. "one" radical in Chinese characters (Kangxi radical 1)
  7. also pr. yāo for greater clarity when spelling out numbers digit by digit
2 诺 nuò
  1. to consent
  2. to promise
  3. (literary) yes!
3 千金 qiānjīn
  1. thousand jin 斤 (pounds) of gold
  2. money and riches
  3. (honorific) invaluable (support)
  4. (honorific) daughter