一言为定
yī yán wéi dìng
It’s a deal.
Character by character
一yī
one
one
言yán
word
word
为wéi
become
become
定dìng
settled
settled
Example
好，一言为定，明天早上八点见！
Right, it’s a deal — see you at eight tomorrow morning!
Tone: neutral.
Usage and origin
Seals a promise in conversation; 为 is wéi here.
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