Clerical dignitary blowing top immediately (4)
I believe the answer is:
anon
'immediately' is the definition.
(thesaurus)
'clerical dignitary blowing top' is the wordplay.
'clerical dignitary' becomes 'canon'.
'blowing top' means to remove the first letter.
'canon' with its initial letter taken away is 'ANON'.
(Other definitions for anon that I've seen before include "Presently - or unknown" , "In due course" , "Nameless (abbr.); soon" , "coming after a call" , "Having no known name" .)