Adjective:

1. based on custom rather than documentation;

   "an unwritten law"
   "rites...so ancient that they well might have had their unwritten origins in Aurignacian times"
   

2. using speech rather than writing;

   "an oral tradition"
   "an oral agreement"
   

3. said or done without having been planned or written in advance;

   "he made a few ad-lib remarks"
   

oraladj.口头的；口部的；口语的n.口试

spokenadj.口语的动词speak的过去分词.

unrecordedadj.未记录下来的；未入账的

vocaladj.声音的；口头的；声乐的；直言不讳的n.元音；声乐作品

understoodadj.懂得的；不言自明的动词understand的过去式和过去分词.

acceptedadj.公认的；录取的；可接受的；已承兑的

traditionaladj.传统的

tacitadj.心照不宣的；缄默的；默示的

knownadj.已知的；有名的动词know的过去分词.

ad-libv.即兴演唱；临时穿插；信口说出n.即兴表演adj.即兴表演的；临时插入的.

spontaneousadj.自发的，自然的，本能的；自然产生的

writtenadj.书面的；写成文字的动词write的现在分词形式.

1. This is an unwritten constitution.
   这是一个不成文的法规。
2. He bore the unwritten rule in mind.
   他牢记那条不成文的规矩。
3. The missive remains unwritten and unsent.
   这件公文未写也未发出去。
4. This assignment will examine Britain's peculiar unwritten constitution.
   这篇文章将审查英国的有意思的没记录的宪法。