cantrip

cantrip \KAHN-trip\, noun:

1. Chiefly Scot. A magic spell; trick by sorcery.
2. Chiefly British. Artful shamming meant to deceive.

Used properly, it may be possible to drive a vampire or garou into frenzy with this cantrip.
-- Steve Long, Ethan Skemp, Combat

And before I knew it her arms were around me, and she smelt of lavender and delicious silk, and her voice in my ear was whispering something—a cantrip, I thought, with a twist of surprise, a cantrip, just like the days in Lansquenet—and then I looked up and it wasn't Maman there at all.
-- Joanne Harris, The Girl with No Shadow: A Novel

Cantrip is of uncertain origin, but it is most likely a variation of the Old English word calcatrippe which referred to both a plant and a type of iron ball used to block calvary in warfare.