Literal meaning
one (一) — promise (诺) — thousand (千) — gold (金)
Origin
Records of the Grand Historian (《史记·季布栾布列传》). Ji Bu (季布), a general of the early Han dynasty, was famous for always keeping his word. There was a saying about him among contemporaries: 得黄金百斤，不如得季布一诺 — "Receiving a hundred catties of gold isn't as valuable as getting one promise from Ji Bu." His personal integrity literally became more valuable than money. The phrase has carried that reputation forward for two millennia.
Examples
Usage & nuances
Strong endorsement of integrity. Works in business contexts ("his word is gold") and personal ("trustworthy to the bone"). Wouldn't apply to ordinary follow-through — reserved for unusually high reliability.
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