Heterodoxy (6)
I believe the answer is:
heresy
'heterodoxy' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for heresy that I've seen before include "Unorthodox doctrine" , "Religious unorthodoxy" , "Yes her (anag.)" , "Opinion opposed to conventional belief" , "Opinion contrary to those of orthodox religion" .)