When one is arranged as part of a games event or competition.
Olympic Decathlon happened in 1981.
The Activision Decathlon happened in 1983.
Intellectual Decathlon happened in 1984.
Daley Thompson's Decathlon happened in 1984.
Bruce Jenner's World Class Decathlon happened in 1996.
The correct spelling is decathlon.
A decathlon :)
The word decathlon does not have an antonym.
Olympic Decathlon was created in 1980.
The Last Decathlon was created in 1980.
Intellectual Decathlon was created in 1984.
Decathlon Group was created in 1976.