Any of various units of distance, including the statute mile of 5,280 ft (1.61 km). It originated from the Roman mille passus, or thousand paces, which measured 5,000 Roman ft (4,840 English ft [1.475 km]). A nautical mile is the length on the Earth's surface of one minute of arc or, by international definition, 1,852 m (6,076.12 ft [1.1508 statute mi]); it remains in universal use in both marine and air transportation. A knot is one nautical mile per hour. See alsoInternational System of Units; metric system.