Antagonistic

google

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late 16th century: from French antagoniste or late Latin antagonista, from Greek antagōnistēs, from antagōnizesthai ‘struggle against’ (see antagonize).

wiktionary

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From antagonist +‎ -ic.

etymonline

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antagonistic (adj.)

"acting in opposition," 1630s, from antagonist + -ic. Related: Antagonistical (1620s); antagonistically.