Thoughts formerly admitted by upstanding pious person, politically correct (8)
I believe the answer is:
concepts
'thoughts' is the definition.
(concept is a kind of thought)
'formerly admitted by upstanding pious person politically correct' is the wordplay.
'formerly' becomes 'once' (synonyms).
'admitted by' is an insertion indicator.
'upstanding' shows that the letters should be reversed in order.
'pious person' becomes 'st' (saint).
'politically correct' becomes 'PC'.
'st'+'pc'='stpc'
'stpc' in reverse letter order is 'cpts'.
'once' put within 'cpts' is 'CONCEPTS'.
(Other definitions for concepts that I've seen before include "'Abstract ideas, thoughts (8)'" , "Abstracts or general ideas" , "Abstract or general idea" , "Abstract or general ideas" .)