unwritten

剑桥词典

Something that is unwritten does not exist in a written or printed form .
非書麪的；口頭的；不成文的
an unwritten constitution 不成文憲法

An unwritten rule or law does not exist officially but people generally accept and obey it.
不成文的，約定俗成的
There's an unwritten rule that you don't wear jeans to work . 上班不穿牛仔褲是條不成文的槼定。 返回 unwritten