Stun was a spell acquired and used by Kain during the events of Blood Omen: Legacy of Kain. It was located in a cave next to the entrance of the Oracle's Cave, and allowed Kain to throw a harmless, homing magic projectile to disable human enemies, rendering them in a waver state for a time and letting Kain to feed upon them. This spell had no effect on bosses, but could be used to instantly kill weaker human ghosts.
Enemies disabled by this spell would remain in a waver state longer that if they were stunned by Kain's mace.
Like many of Kain's Blood Omen spells, Stun is not seen in further games.