Memorial of old priest outwardly Roman Catholic (5)
I believe the answer is:
relic
'memorial' is the definition.
(object kept to remember a holy person)
'old priest outwardly roman catholic' is the wordplay.
'old priest' becomes 'eli' (Biblical character).
'outwardly' indicates putting letters inside (some letters go outside others).
'roman catholic' becomes 'rc' (abbreviation for Roman Catholic).
'eli' inserted within 'rc' is 'RELIC'.
'of' acts as a link.
(Other definitions for relic that I've seen before include "Object of historic interest" , "Holy fragment as of saint" , "Reminder of times past" , "Left over item, sometimes sacred" , "for remembrance" .)