1、Its a deal ：一言为定 。
2、Thats settled then：一言为定
3、count it as settled：一言为定
例句：
“一言为定了。”外祖父说。
\" That\'s settled,\" said the grandfather.
那样我就可以一言为定地告诉你了。
So that I may tell you decisively.
阿美：一言为定，你没有开玩笑，是吧？
May: That\'s great! You are not kidding, are you
