In Vampire: The Masquerade, this is the unique discipline of Clan Assamite -- which, given Webster 1913's definition, is appropriate, since the Assamites are a clan of assasins.

Quietus is a powerful discipline, and most of its uses devoted to making murder easier. The first level, for instance, creates a radius of silence around the user, allowing her to move inaudibly -- and her victim quite unable to call for help. Higher levels allow her to poison blades or inflict damage from a distance after having touched her victim.