Will’s statement rubbished (9)
I believe the answer is:
testament
'will's' is the definition.
('testament' can be a synonym of 'will')
'statement rubbished' is the wordplay.
'rubbished' indicates an anagram.
'statement' with letters rearranged gives 'TESTAMENT'.
(Other definitions for testament that I've seen before include "it could be old or new" , "New and old parts of the Bible" , "(Person's) will" , "Written statement of wishes" , "with 1a [NEW] where is Mark?" .)