The Mississippi River, derived from the old Ojibwe word misi-ziibi meaning 'great river' (gichi-ziibi 'big river' at its headwaters), is the second-longest named river in North America, with a length of 2320 miles (3733 km) from Lake Itasca to the Gulf of Mexico. The longest named river in North America is its tributary, the Missouri River, with a length of 2341 miles (3767 km) from the confluence of the Jefferson, Madison, and Gallatin to the Mississippi River. Taken together, the Jefferson, Missouri, and Mississippi form the largest river system in North America.
If measured from the source of the Jefferson to the Gulf of Mexico, the length of the Mississippi-Missouri-Jefferson combination is approximately 3900 miles (6275 km), making the combination the 3rd longest river in the world. The uppermost 207 mi (333 km) of this combined river are called the Jefferson, the lowest 1352 mi (2175 km) are part of the Mississippi, and the intervening 2341 mi (3767 km) are called the Missouri.