Sometimes, the connection between a borrowed name and the character that bears that name isn’t always clear. Dumbledore, the name given to the headmaster of Hogwarts and one of the preeminent wizards of the Potter universe, is an 18th-century word for a bumblebee:
What is the burnie-bee? Is it not the humble-bee, or what we call the “dumble dore,”—a word whose descriptive droning deserves a place in song?
—Robert Southey, letter, 12 March 1799
Dumble- was a prefix that was used to refer to various insects, and it has close cousins in humble-, bumble-, and dummel-, which some etymologists tie to dumb. Dore, or dor, is a word that dates back to almost 700 AD and refers to bees or flies. Bumblebees, with their bobbing, wavering, slow flight, might have looked dull or lazy, which accounts for the combination of dore and the dumb-adjacent prefix dumble-.
What about Rowling? Is she somehow implying that Albus Dumbledore is lazy or dull? Not at all:
“Dumbledore” is an old English word meaning bumblebee. Because Albus Dumbledore is very fond of music, I always imagined him as sort of humming to himself a lot.
—J.K. Rowling, in interview with Christopher Lydon on “The Connection”, WBRU Radio, 12 Oct. 1999