Gymnast

google

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late 16th century: from French gymnaste or Greek gumnastēs ‘trainer of athletes’, from gumnazein ‘exercise naked’ (see gymnasium).

wiktionary

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From Ancient Greek γυμναστής(gumnastḗs, “trainer of athletes”), from γυμνάζω(gumnázō, “I train naked, exercise”), from γυμνός(gumnós, “naked”)

etymonline

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gymnast (n.)

1590s, "one who is expert in gymnastics," a back-formation from gymnastic. Greek gymnastes was "a trainer of professional athletes."