from the greek “athlon” - prize -> athlein - wanting a prize -> athlētēs- one who competes for a prize -> athleta - Latin version -> modern English (note similarity between athlētēs and athletes)

Although the physical side is culturally connotated, there’s nothing in the strict definition that requires “someone who competes for a prize” to be a physical, e.g. chess, math, science, economics…competitor