noun: 1. A footrace of 26 miles, 385 yards (42.195 km). 2. Any long-distance race, for example, a swimming marathon. 3. An endurance event or contest, such as a dance marathon. 4. An event of greater than usual length, for example, a Netflix marathon. adjective: Relating to something that requires a lot of effort and endurance. verb tr.: To take part in a long race, task, event, etc., or one that requires long sustained effort.