unwritten law

n. [律]不成文法, 习惯法

例句与用法：

It's an unwritten law around here that everyone fetches his own coffee, even the managers.

这儿有一条不成文法，即每人自己去取咖啡，哪怕是经理也是如此。

详细释义：

ph.

习惯法, 不成文法