Ne·gro(nā′grō, nĕ′grō, -gro͝o), Río
1. A river rising in central Argentina and flowing about 645 km (400 mi) eastward to the Atlantic Ocean.
2. A river rising in southern Brazil and flowing about 805 km (500 mi) generally southwest to the Uruguay River in southwest Uruguay.
3. A river of northwest South America flowing about 2,255 km (1,400 mi) from eastern Colombia to the Amazon River near Manaus, Brazil. Part of its course forms a section of the Colombia-Venezuela border.