a promise is worth a thousand gold pieces; a promise must be kept at all costs
A yojijukugo emphasizing the absolute weight of one's word; used in formal or literary contexts to stress that a promise should never be broken.
With the spirit of 'a promise worth a thousand gold,' he always keeps even the smallest promises.
As the saying goes, 'a promise is worth a thousand gold pieces,' so once you make a promise, you should keep it no matter what.
約束 is the common word for 'promise'; 一諾千金 is a literary set phrase stressing the supreme value of keeping a promise.
千金 literally means 'a thousand pieces of gold' and appears in other idioms to indicate great value, but 一諾千金 is a fixed yojijukugo.
A yojijukugo derived from classical Chinese literature, combining 一諾 (one promise) and 千金 (a thousand gold pieces) to express that a single promise is as valuable as a fortune.