Or so says the OED -- and pretty much no other dictionary. This has led to much speculation about whether the OED compilers are having us on. The Guelphs and the Ghibellines were, of course, political parties in 11th and 12th century Italy, familiar to anyone who's read Dante (you can tell which side he was on as all the Ghibellines that show up in Il comedia are in the first book) but otherwise mostly forgotten by popular history except as a funky phrase. I, like just about everyone, learned of the word thanks to Ammon Shea citing it as perhaps his favorite definition in the OED in Reading the OED: One Man, One Year, 21,730 Pages. (Which is not the same as his favorite word, mind -- he was impressed by its initial incomprehensibility.)
The headmaster easily disghibellined the troublemakers from the rest of the class by the scratches on their faces.