From WordNet (r) 2.0 (August 2003) [wn]:
marathon
n 1: any long and arduous undertaking [syn: endurance contest]
2: a footrace of 26 miles 385 yards
3: a battle in 490 BC in which the Athenians and their allies
defeated the Persians [syn: Marathon, {battle of
Marathon}]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
marathon \marathon\ n.
1. A footrace of 26 miles 385 yards. [WordNet sense 2]
[WordNet 1.5]
2. Hence: Any long and arduous undertaking, straining the
endurance of the participants. [WordNet sense 1]
Syn: endurance contest.
[WordNet 1.5]
3. (Capitalized)a battle in 490 BC in which the Athenians and
their allies defeated the Persians. [WordNet sense 3]
Syn: battle of Marathon.
[WordNet 1.5]