The most common and most likely answer to this crossword clue is the 9 letter word TESTAMENT
I've seen this crossword clue in Financial Times
T
E
S
T
A
M
E
N
T
More clues leading to the result TESTAMENT
- Will roused mates in canvas shelter
- Will’s statement rubbished
- Will meant to be changed during trial
- Grisham’s novel account sending up vacuous thickie
- Will Shakespeare originally cutting offensive last word at end of Hamlet
- Will trial with a group of chaps lead to trouble?
- Will trial mean different result, ultimately?
- Mates larking around under canvas in books, with 1A
- Legal document for international meant to be played
- Witness mates, hammered, opening old wine
Buddy explains!

The straight part
We know that "Legal document" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case legal document = testament.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TESTAMENT mean?
TESTAMENT noun- A solemn, authentic instrument in writing, by which a person declares his or her will as to disposal of his or her inheritance (estate and effects) after his or her death, benefiting specified heir(s).
- One of the two parts to the scriptures of the Christian religion: the New Testament, considered by Christians to be a continuation of the Hebrew scriptures, and the Hebrew scriptures themselves, which they refer to as the Old Testament.
- A tangible proof or tribute.
- A credo, expression of conviction