It's thought that the word athlete entered English in the early fifteenth century; the first attestation listed in the OED is from 1425, in reference to wrestlers. That came from Latin athleta, which referred to anyone who competed in public games, and goes back to the Ancient Greek verb athlein, which meant "to compete for prizes". This was a conjugation of either athlon, meaning "prize", or athlos, meaning "competition". Officially, those related terms have an unknown origin, but some linguists reconstruct it to the Proto-Indo-European root hweh, which meant "to wheeze" (the connection being a tenuous one to athletes getting exhausted). Usage of the word athlete in literature over time rapidly increased in the twentieth century due to greater interest in sports in general.
Hello! I'm Adam Aleksic, a sophomore studying government and linguistics at Harvard University, where I co-founded the Harvard Undergraduate Linguistics Society. In addition to etymology, I also really enjoy politics, vexillology, geography, board games, conlanging, and law.