That woman, see, is wrong - unacceptable beliefs (8)
I believe the answer is:
Here is my best explanation:
'unacceptable beliefs' is the definition.
The answer and definition can be both related to thinking as well as being plural nouns.
Maybe there's an association between them I don't understand?
'that woman see is wrong' is the subsidiary indication.
'that woman' becomes 'her' (I've seen this before**).
'wrong' indicates an anagram.
'seeis' anagrammed gives 'esies'.
(Other definitions for heresies that I've seen before include "Beliefs that reject the orthodox tenets of a religion", "unacceptable beliefs" and "Series he composed about anti-religious opinions".)