Sacrament possibly such a rite (9)
I believe the answer is:
eucharist
'sacrament' is the definition.
(I know that Eucharist is a type of sacrament)
'possibly such a rite' is the wordplay.
'possibly' indicates anagramming the letters.
'such'+'a'+'rite'='sucharite'
'sucharite' is an anagram of 'EUCHARIST'.
(Other definitions for eucharist that I've seen before include "Consecrated bread" , "church service" , "Mass" , "Bread and wine" , "Holy Communion" .)