Heretical movement beyond control after number retired (7)
I believe the answer is:
gnostic
'heretical' is the definition.
(thesaurus)
'movement beyond control after number retired' is the wordplay.
'movement beyond control' becomes 'tic' (a tic is an involuntary movement).
'after' is a charade indicator (letters next to each other).
'number' becomes 'song' (I've seen this before).
'retired' says the letters should be written in reverse.
'song' backwards is 'gnos'.
'tic' after 'gnos' is 'GNOSTIC'.
(Other definitions for gnostic that I've seen before include "Having special mystical knowledge, costing a lot" , "Occult" , "Relating to mystical knowledge" .)