a river in northeast Africa, the longest river in the world, whose water is used for most of the farming in Egypt and Sudan. It is formed from two rivers: the Blue Nile, which starts in Ethiopia, and the White Nile, which starts in Uganda. The two rivers join in Sudan, and flownorth into the MediterraneanSea. In Egypt, the Nile is popular with tourists, who sail up and down it on large boats, visiting places such as Cairo and Karnak.