Prior to start paying Reverend debts with extreme loyalty (10)
I believe the answer is:
previously
'prior' is the definition.
(synonyms)
'start paying reverend debts with extreme loyalty' is the wordplay.
'start' indicates taking the first letters.
'reverend' becomes 'rev' (I am not sure about this - if you are sure you should believe this answer much more).
'debts' becomes 'IOUs' (promises to pay debts).
'with' says to put letters next to each other.
'extreme' says to hollow out the word (remove centre letters).
'loyalty' with its centre removed is 'ly'.
The first letter of 'paying' is 'p'.
'p'+'rev'+'ious'+'ly'='PREVIOUSLY'
'to' is the link.
Can you help me to learn more?
(Another definition for previously that I've seen is " Hitherto".)