Fake copy finally found in battered tin chest (9)
I believe the answer is:
synthetic
'fake' is the definition.
(I've seen this in another clue)
'copy finally found in battered tin chest' is the wordplay.
'finally' suggests the final letters.
'found in' indicates putting letters inside.
'battered' indicates an anagram.
The last letter of 'copy' is 'y'.
'tin'+'chest'='tinchest'
'tinchest' is an anagram of 'snthetic'.
'y' going within 'snthetic' is 'SYNTHETIC'.
(Other definitions for synthetic that I've seen before include "Affected" , "ersatz" , "Not genuine, unnatural" , "Artificially produced" , "Artificially-made compound" .)