Once more saint is in opposition (7)
I believe the answer is:
against
'is in opposition' is the definition.
(I've seen this before)
'once more saint' is the wordplay.
'once more' becomes 'again' (synonyms).
'saint' becomes 'st' (abbreviation).
'again'+'st'='AGAINST'
(Other definitions for against that I've seen before include "Placed in direct contact with" , "Anti, touching" , "Con" , "Facing" , "V" .)