Lethargic prisoner conceals naked panic (9)
I believe the answer is:
inanimate
'lethargic' is the definition.
(thesaurus)
'prisoner conceals naked panic' is the wordplay.
'prisoner' becomes 'inmate' (inmate can mean someone in prison).
'conceals' means one lot of letters goes inside another.
'naked' says to take the centre (outside letters removed so centre is unclothed).
The central letters of 'panic' are 'ani'.
'inmate' going around 'ani' is 'INANIMATE'.
(Other definitions for inanimate that I've seen before include "Showing no sign of life" , "Not living" , "Dull" , "Without life" , "spiritless" .)