Hostile once more by the way (7)
I believe the answer is:
against
'hostile' is the definition.
(thesaurus)
'once more by the way' is the wordplay.
'once more' becomes 'again' (synonyms).
'by the way' becomes 'st' (I've seen this in other clues).
'again'+'st'='AGAINST'
(Other definitions for against that I've seen before include "In disagreement with" , "on the other side" , "In conflict with" , "Placed in direct contact with" , "Not favouring" .)