Initiation rite (7)
I believe the answer is:
baptism
'initiation rite' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for baptism that I've seen before include "Christian sacrament that symbolises admission to the church" , "Church admission rite" , "Initiation; christening" , "Religious rite involving water" , "Christian sacrament requiring pouring of water" .)