Christian emblem (5,3)
I believe the answer is:
agnus dei
'christian emblem' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for agnus dei that I've seen before include "Part of the ordinary" , "Emblem of Christ" , "Part of Latin Mass" , "part in requiem" , "'Latin mass prayer, Lamb of God (5,3)'" .)