Jack's answer: 'Pardon?' (10)
I believe the answer is:
absolution
'pardon?' is the definition.
(thesaurus)
'jack's answer' is the wordplay.
'jack' becomes 'ab'.
'answer' becomes 'solution' ('solution' can be a synonym of 'answer'**).
'ab'+'solution'='ABSOLUTION'
(Other definitions for absolution that I've seen before include "pardon" , "acquittal" , "Forgiveness" , "discharge" , "Release from guilt" .)