The word "marathon" is correct and usable in written English.
You can use it when referring to a long-distance running event, as in the sentence: "I recently ran a marathon and it took me six hours!".
Congratulations on your achievement [Fiennes became the oldest Briton ever to complete the Marathon des Sables ultra-marathon race in the Sahara last Friday].
At 92, Harriette Thompson has become the oldest woman to run a marathon after completing the Rock'n'Roll marathon in San Diego in 7hr 24min.
Not only that, but Thompson only ran her first marathon at the age of 76, proving that it's never too late to start.
I'd love to try and do a marathon at some point.
Then a few weeks later the border reopened, the marathon was back on and the tour companies creaked back into action.
Kiev and pro-Russia rebels agreed a peace roadmap on 12 February after marathon negotiations in Minsk involving the leaders of France, Germany, Russia and Ukraine.
Simon has recently run a marathon, in just over four hours, so he's become my absolute hero and now I'm on that tip too.
The three-hour broadcast opened with a monologue from host Seth Meyers, announcing his plans to trump the UK version of the fundraising marathon.
The Doctor can tell when the marathon season is upon us.
It's always a thriller, always a marathon".
Two years after rising to national prominence with a 13-hour talking filibuster against drones, Rand Paul has made another marathon speech on the floor of the US Senate – only this time in a bid to halt the federal government's mass surveillance of Americans' phone records and to derail an extension of the Patriot Act.
