IPA: /hɛpˈθæθliːt/
KK: /ˈhɛp.tæθ.liːt/
A person who participates in a sports event consisting of seven different track and field events.
The heptathlete trained hard to improve her performance in each of the seven events.
Heptathlete → It is formed from "hepta-" (from Greek "heptá", meaning seven) and "athlete" (from Greek "athlētēs", meaning one who competes for a prize). The word refers to an athlete who competes in seven different track and field events.
Think of 'seven' ('hepta-') events that an 'athlete' competes in — that's what a heptathlete does.