In this place, spout your primarily unorthodox opinions (6)
I believe the answer is:
heresy
'in this place spout your primarily unorthodox opinions' is the definition.
The answer and definition can be both related to thinking as well as being singular nouns.
Maybe there's an association between them I don't understand?
'in this place spout your primarily' is the wordplay.
'in this place' becomes 'here' (synonyms).
'primarily' suggests taking the first letters.
The first letters of 'spout your' is 'sy'.
'here'+'sy'='HERESY'
Can you help me to learn more?
(Other definitions for heresy that I've seen before include "Unorthodox religious belief" , "Opinion contrary to generally accepted beliefs" , "Deviation from orthodox religious thinking" , "you shouldn't believe it" , "Yes her (anag.)" .)