The most likely explanation of this name is that it means lord of the dwelling/house.
Beelzebul would then be referring to the chief of those spirits who made their home or dwelt in those possessed by them (see also Matthew 10:25).1 Here in Matthew 12:24 the Pharisees specifically invoke the less commonly known name Beelzebul because it provided them with an aura of specialized knowledge regarding the inner workings of the kingdom of darkness.2
25 Comme Jésus connaissait leurs pensées, il leur dit: Tout royaume divisé contre lui-même est dévasté, et toute ville ou maison divisée contre elle-même ne peut subsister.