Dissident bishop appearing in part of film (5)
I believe the answer is:
rebel
'dissident' is the definition.
(rebel is a kind of dissident)
'bishop appearing in part of film' is the wordplay.
'bishop' becomes 'b' (abbreviation used in chess).
'appearing in' means one lot of letters goes inside another.
'part of film' becomes 'reel' (I've seen this before).
'b' put within 'reel' is 'REBEL'.
(Other definitions for rebel that I've seen before include "One resisting authority" , "One who rises up" , "Rise up - dissent" , "Maverick" , "Resist authority" .)