To leap upon, spring upon, or pounce. Used only once in the New Testament — in the dramatic account of the sons of Sceva, when the demon-possessed man leapt on the seven would-be exorcists and overpowered them all. The word conveys sudden, violent, overwhelming force.
Ephallomai serves as a stark warning about spiritual authority and presumption. The sons of Sceva tried to use Jesus's name as a magic formula without personal relationship with Him. The demon's response — 'Jesus I know, and Paul I know about, but who are you?' — followed by the man leaping on them, demonstrates that spiritual warfare is not a game. Authority comes from relationship, not ritual. Borrowed authority is no authority at all.