Will roused mates in canvas shelter (9)
I believe the answer is:
testament
'will' is the definition.
(synonyms)
'roused mates in canvas shelter' is the wordplay.
'roused' indicates anagramming the letters (I've seen this in other clues).
'in' indicates putting letters inside.
'canvas shelter' becomes 'tent' (I've seen this before).
'mates' with letters rearranged gives 'estam'.
'estam' placed inside 'tent' is 'TESTAMENT'.
(Other definitions for testament that I've seen before include "Scripture" , "books, with 1a [OLD]" , "Will - part of bible" , "Written statement of wishes" , "Proof" .)