The last name is actually not that fancy. As this old interview with Rowling states:
> How did you decide what to name your characters and places?
>
> I collect unusual names. I have notebooks full of them. Some of the names I made up, like Quidditch, Malfoy. Other names mean something -- _**Dumbledore, which means "bumblebee" in Old English...seemed to suit the headmaster, because one of his passions is music and I imagined him walking around humming to himself.**_ And so far I have got names from saints, place-names, war memorials, gravestones. I just collect them -- I am so interested in names.
(Barnes and Nobles Interview with J.K. Rowling (1999); Emphasis mine)