Baptism or matrimony (4)
I believe the answer is:
rite
I believe this clue is a double definition.
'baptism' is the first definition.
(I've seen this in another clue)
'matrimony' is the second definition.
(I've seen this in another clue)
(Other definitions for rite that I've seen before include "Customary observance" , "something like mass" , "Ceremony - ritual" , "Formal procedure" , "Established religious ceremony" .)