The Collaborative International Dictionary of English v.0.48:

Cantrap \Can"trap\, Cantrip \Can"trip\, n. [Cf. Icel. gandar,
   ODan. & OSw. gan, witchcraft, and E. trap a snare, tramp.]
   A charm; an incantation; a shell; a trick; adroit mischief.
   [Written also cantraip.] [Scot.]
   [1913 Webster] Cantred