The SND has "brank" as a 15th century verb. But Hogg's printed "brankie" was a noun in the 19th - a noun that, as far as I can discover, appears nowhere outside of this song and discussions of it. That would be rather curious if it were authentic.

Of course words can have more than one meaning. But the genuine to "brank" and the suspicious "brankie" are two different words (spelled and pronounced differently) besides being two different parts of speech. They have different meanings. Think of English "mug" (a bloke) and "muggy" (humid). One cannot deduce the meaning of either one just from looking at the spelling and meaning of the other.

Much the same goes for "brank" and "brankie." "To behave violently" is not the same idea as "a battle." The ideas are not interchangeable - though they would obviously be related *if* "brankie" were real.

But would Hogg use a word that none of his readers who was less than 400 years old would understand?

I believe people sing "brankie" instead of "bankie" because most of them are afraid to change the received lyrics. Non-Scots are unlikely even to think of "bankie," a natural coinage in Scots but not in other forms of English. (It's too bad that "bankie" doesn't appear anywhere else either, but at least it fits the context with no distortion of meaning or grammar.)

Of the two choices available, only "bankie" makes sense in Hogg's line. Perfect sense, in fact. (This is the kind of interpretation that editors of Shakespeare have to do all the time: the earliest printings of the plays are often a mess of misprints and apparently imaginary words.)

Of course, if anyone can find even *one* clear example of "brankie" used before James Hogg as a real noun meaning "strife or battle" or anything like it, I will happily change my opinion.

Because then the mystery will have been solved.