Reverie, free, about introduction of politic postponement (8)
I believe the answer is:
reprieve
'postponement' is the definition.
(I have seen 'Postponement of punishment' mean 'reprieve' so perhaps 'postponement' could also mean 'reprieve')
'reverie free about introduction of politic' is the wordplay.
'free' indicates anagramming the letters.
'about' indicates putting letters inside.
'introduction of' indicates taking the first letters.
The initial letter of 'politic' is 'p'.
'reverie' is an anagram of 'rerieve'.
'rerieve' enclosing 'p' is 'REPRIEVE'.
(Other definitions for reprieve that I've seen before include "Delay or cancel punishment" , "cancellation of death warrant" , "Postpone punishment for the time being" , "Postponement of the death sentence" , "Temporary relief, like stay on death sentence" .)