The name Beelzebub in the Bible
Beelzebul is the English transliteration of the Greek word for Baal Zebub, and Beelzebub is a bit of a hybrid of the two. Beelzebub, or Beelzebul, is the New Testament name for satan, a.k.a the devil (Matthew 10:25).
Etymology of the name Beelzebub
The second part of the name Beelzebub comes from the Hebrew noun זבוב (zebub), meaning fly:
Beelzebub literally means Lord Of The Fly but in this case, the singular should be interpreted with an English plural (for instance: the phrase "king of the Amalekites" would in Hebrew be written as "king of the Amalekite").
Beelzebub means Lord Of The Flies but since flies accept no central rule, it's an empty or even mock title.
Also see our article on the pseudo-name Lucifer.