The Hobbits of the Shire originally gave it the punning name Branda-nîn, meaning "border water" in original Hobbitish Westron. This was later punned again as Bralda-hîm meaning "heady ale" (referring to the colour of its water), which Tolkien renders into English as Brandywine.[4]
The word Brandywine both resembles the original Elvish name Baranduin, and provides the Hobbitish meaning adequately.
The word brandywine was actually the archaic English word for brandy as imported from the Dutch brandewijn. David Salo noted that it represents a possible Old English *baernedwin, meaning "burned wine", which would resemble quite closely the original Elvish Baranduin,[5] making Hobbitish Brandywine a legitimate corruption of S. Baranduin.
I’m just.... I have no words. Language nerd/master JRRT strikes again