IPA: //traɪˈæθliːt//
KK: /traɪˈæθlit/
A person who participates in a triathlon, which is a race that includes swimming, cycling, and running.
She trained for months to become a successful triathlete.
Triathlete → It is formed from "tri-" (meaning three) and "athlete" (from Greek "athlētēs", meaning one who competes for a prize). The word "triathlete" refers to a person who competes in three different sports, typically swimming, cycling, and running.
Think of someone competing in 'three' ('tri-') different sports, which is what a triathlete does.