1876, in writings on Greek drama, "a hero (attacked in the play by an antagonist)," from Latin agonista, Greek agonistes "rival combatant in the games, competitor; opponent (in a debate)," also, generally "one who struggles (for something)," from agonia "a struggle for victory" (in wrestling, etc.), in a general sense "exercise, gymnastics;" also of mental struggles, "agony, anguish" (see agony). Agonistes as an (ironic) epithet seems to have been introduced in English by T.S. Eliot (1932).
<a href="https://www.etymonline.com/word/agonistic">Etymology of agonistic by etymonline</a>
Harper, D. (n.d.). Etymology of agonistic. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/agonistic