Beelzebul: a name for the prince of the demons, used by Jesus's accusers
Beelzebul appears only in one dispute in the Gospels. After Jesus drives out a demon, his opponents charge that he does it in league with the chief of the demons, whom they call Beelzebul. All seven uses point to that one figure: the head of the evil spirits, the power the accusers say Jesus is secretly working for.
The name itself is an old title that once belonged to a Canaanite god, meaning something like "lord of the lofty dwelling" or "the prince." By Jesus's day Jewish speakers had turned that title into a name for the ruler of the demons. The wordplay in one saying makes the sense clear: Jesus warns that if people have called the master of the house "Beelzebul," they will say worse about his household, and the joke only works if the name means "lord of the house," not "lord of the flies."
When Jesus answers the charge, he does not repeat the name his opponents used. He swaps it for a different one, Satan (Σατανᾶς), meaning "the adversary," and argues that a kingdom or a household divided against itself cannot stand. The switch is deliberate: it moves the argument off the ground of pagan gods and onto the question of whose kingdom is arriving.