SYN: Adversary, opponent, rival, competitor, foe, enemy.
ANT: Aider, abettor, accomplice, accessory, ally.
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KEY: Antagonistic.
SYN: Adverse, opposing, inimical, hostile, repugnant, contrary.
ANT: Favoring, aiding, harmonious, friendly, agreeable to.
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KEY: Antecedence.
SYN: Anteriority, priority, precursorship, premonition, Introduction, preparation, pre-existence.
ANT: Posteriority, subsequence, succession, sequel, supervention, consequence.