A river that flows for 600 miles (970 km) across western Arkansas and into northern Louisiana, where it is known in part as the Black River and empties into the Red River.
Definition of Ouachita River in US English:
Ouachita River
proper noun
A river that flows for 600 miles (970 km) across western Arkansas and into northern Louisiana, where it is known in part as the Black River and empties into the Red River.