n.1 a long-distance running race, usu. of 26 miles 385 yards (42.195 km).
2 a long-lasting or difficult task, operation, etc. (often attrib.: a marathon shopping expedition).
Derivatives:
marathoner n.
Etymology: Marathon in Greece, scene of a victory over the Persians in 490 BC: a messenger was said to have run to Athens with the news, but the account has no authority