1. A humble-bee or bumble-bee
2. A cockchafer
Let me start this off by saying I know little to nothing about Harry Potter. BUT, I'm pretty sure this is a character in the book.
The word is first attested in 1787 as a dialect word in parts of the UK meaning "bumble bee." It comes from the combination form dumble-, which varies with bumble-, drumble-, and humble-. All the forms have the same meaning as dummel, which is a dialectal word meaning "stupid, dull, slow."
Which dumbledore do you prefer?