Sanctify, make holy (5)
I believe the answer is:
bless
This clue is a double definition.
'sanctify' is the first definition.
(synonyms)
'make holy' is the second definition.
(I've seen this before)
(Other definitions for bless that I've seen before include "Order of service" , "Give benediction" , "Approve of" , "Glorify" , "Sanctify" .)