1. a long-distance running race of 26.2 miles (42.2 kilometers)
2. any long and difficult task or activity that requires great endurance

1. lasting for a very long time; requiring great endurance

Examples

• She trained for months before running her first marathon.
• The Boston Marathon attracts thousands of runners each year.
• Writing the novel was a marathon that took him three years.
• The budget negotiations turned into a marathon session lasting all night.
• They held a marathon meeting to resolve the crisis.
• The marathon exam lasted four hours.
• His marathon speech bored the audience.