"Close writ"を調べてみました。
以下、Quick Ref/Glossary からのコピーです。
”Close writ ”
A writ under the Great Seal sent folded and closed by the seal on the outside, so its contents could be read only by the person or persons to whom it was addressed. Unclosed letters, proclamations or writs issued under the Great Seal were termed 'patent'. These were open, with the seal appended on a tag or cord, so the text could be read by any literate person.
Patents, however, existed before the law. The first Italian patent was actually awarded by the Republic of Florence in 1421,[3] and there is evidence suggesting that something like patents was used among some ancient Greek cities.[4]