Bloke with revolutionary knack for incantation (6)
I believe the answer is:
mantra
'for incantation' is the definition.
(a mantra is a spiritual incantation)
'bloke with revolutionary knack' is the wordplay.
'bloke' becomes 'man' (informal term for a man).
'with' is a charade indicator (letters next to each other).
'revolutionary' says the letters should be written backwards.
'knack' becomes 'art' (both can mean a skill or talent).
'art' reversed gives 'tra'.
'man'+'tra'='MANTRA'
(Other definitions for mantra that I've seen before include "what one keeps repeating" , "Sacred text used as incantation" , "Chanted phrase" , "Something said to focus concentration" , "that > may be repeated in reflection" .)