Incredibly uncivil about quietly revolting (12)
I believe the answer is:
surprisingly
'incredibly' is the definition.
(thesaurus)
'uncivil about quietly revolting' is the wordplay.
'uncivil' becomes 'surly' (I've seen this in another clue).
'about' is an insertion indicator.
'quietly' becomes 'p' (p for piano and quiet).
'revolting' becomes 'rising' (rising up).
'p'+'rising'='prising'
'surly' enclosing 'prising' is 'SURPRISINGLY'.
(Other definitions for surprisingly that I've seen before include "Unexpectedly" , "Amazingly" .)