RC was very religious in times gone by (6)
I believe the answer is:
papist
'rc was very' is the definition.
I can't judge whether this definition defines the answer.
'religious in times gone by' is the wordplay.
I cannot really understand how this works, but
'religious' could be 'pi' (british abbreviation for pious) and 'pi' is found within the answer.
'times' could be 'past' (I have seen 'historical times' mean 'past' so perhaps 'times' could also mean 'past') and 'past' is present in the remaining letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for papist that I've seen before include "Scornful word for Roman Catholic sometimes heard in N Ireland" , "Catholic offensively" , "supporter of Catholicism" , "Believer rudely" , "Follower of the Pope" .)