Uruguay River

American Heritage® Dictionary of the English Language, Fourth Edition

1. A river of southeast South America rising in southern Brazil and flowing about 1,609 km (1,000 mi) west and south along the Brazil-Argentina border and the Argentina-Uruguay border to the Río de la Plata.

WordNet 3.0

1. n. a South American river that arises in southern Brazil and flows south to the Rio de la Plata; the northern section forms the boundary between Argentina and Brazil and the southern section forms the boundary between Argentina and Uruguay