Dead prisoner clutching a nail, oddly (9)
I believe the answer is:
inanimate
'dead' is the definition.
(synonyms)
'prisoner clutching a nail oddly' is the wordplay.
'prisoner' becomes 'inmate' (inmate is a kind of prisoner).
'clutching' is an insertion indicator.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
The alternating letters of 'nail' are 'ni'.
'a'+'ni'='ani'
'inmate' going around 'ani' is 'INANIMATE'.
(Other definitions for inanimate that I've seen before include "Not alive" , "Without life" , "unable to move" , "Lacking life" , "Showing no feeling" .)