形容詞 unwritten:

1. based on custom rather than documentation- J.L.T.C.Spence
2. using speech rather than writing
   同義詞：oral
3. said or done without having been planned or written in advance
   同義詞：ad-lib, spontaneous

1. It's an unwritten law around here that everyone fetches his own coffee, even the managers.
   這兒有一條不成文法，即每人自己去取咖啡，哪怕是經理也是如此。
2. A body of unwritten religious precepts.
   教義一整套非書面的宗教概念
3. Britain has an unwritten constitution, and the United States has a written constitution.
   英國有不成文的憲法，美國有成文的憲法。