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Synonyms for Opposing (same or very similar meaning)

WordNet sense 1 (in opposition to (a policy or attitude etc.)):
opposed

WordNet sense 2 (not in favor of (an action or proposal etc.)):
anti

WordNet sense 3 (characterized by active hostility):
opponent

WordNet sense 4 (characterized by enmity or ill will):
hostile


From the ODE community, based on WordNetadd/edit