Unorthodox opinion (6)
I believe the answer is:
heresy
'unorthodox opinion' 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 "Unorthodoxy - apostasy" , "Religious non-conformity" , "Yes her (anag.)" , "Unorthodox religious belief" , "Opinion opposed to conventional belief" .)