Disjointed reverie about prisoner’s initial pardon (8)
I believe the answer is:
reprieve
'pardon' is the definition.
(I know that pardon can be written as reprieve)
'disjointed reverie about prisoner's initial' is the wordplay.
'disjointed' indicates anagramming the letters (letters disjointed and moved around).
'about' is an insertion indicator.
'initial' says to take the initial letters.
The initial letter of 'prisoners' is 'p'.
'reverie' is an anagram of 'rerieve'.
'rerieve' going around 'p' is 'REPRIEVE'.
(Other definitions for reprieve that I've seen before include "Postponement of punishment" , "Punishment cancellation" , "Spare from (eg the death) penalty" , "Suspend a death sentence." , "Cancel the punishment of (someone)" .)