Baranduin was the original Sindarin name of the River Brandywine, meaning “Brown River”.

Appendix F to The Lord of the Rings explains that Brandywine may seem as if it was a hobbit corruption of Baranduin, but Brandywine actually came from the older hobbit-name Branda-nîn, “Border-water”.
Encyclopedia entry originally written by LadyEowyn_Of_Rohan