IPA: /dɪˈkæθlən/
KK: /dɪˈkæθlən/
A sports competition where athletes compete in ten different track and field events, including running, jumping, and throwing.
He trained for months to prepare for the decathlon at the national championships.
Decathlon → It is formed from "deca-" (from Greek "deka", meaning ten) and "athlon" (from Greek "athlon", meaning contest or prize). The word "decathlon" refers to a contest consisting of ten different athletic events.
Think of 'ten' ('deca-') events in a 'contest' ('athlon') — that's what a decathlon is, a competition with ten events.