a river in Africa, rising in S central Burundi in its remotest headstream, the Luvironza: flows into Lake Victoria and leaves the lake as the Victoria Nile, flowing to Lake Albert, which is drained by the Albert Nile, becoming the White Nile at Lake No, then flowing through South Sudan; joined by its chief tributary, the Blue Nile (which rises near Lake Tana, Ethiopia) at Khartoum, and flows north to its delta on the Mediterranean; the longest river in the world. Length: (from the source of the Luvironza to the Mediterranean) 6741 km (4187 miles)