Prisoner's holding it back for close friend (8)
I believe the answer is:
intimate
'close friend' is the definition.
(thesaurus)
'prisoner's holding it back' is the wordplay.
'prisoner' becomes 'inmate' (inmate is a kind of prisoner**).
'holding' indicates putting letters inside.
'back' shows that the letters should be reversed in order.
'it' backwards is 'ti'.
'inmate' going around 'ti' is 'INTIMATE'.
'for' acts as a link.
(Other definitions for intimate that I've seen before include "Familiar; imply" , "state" , "Private and personal like close acquaintanceship" , "Bosom" , "Make known" .)