Priest enthralled by Roman Catholic memorial (5)
I believe the answer is:
relic
'memorial' is the definition.
(object kept to remember a holy person)
'priest enthralled by roman catholic' is the wordplay.
'priest' becomes 'eli' (biblical figure).
'enthralled by' indicates putting letters inside ('enthral' can mean 'capture').
'roman catholic' becomes 'RC' (abbreviation for Roman Catholic).
'eli' put into 'rc' is 'RELIC'.
(Other definitions for relic that I've seen before include "Bit of a saint, perhaps" , "Surviving ancient custom" , "Piece left over" , "precious object" , "(Holy) remains" .)