Magick is an Early Modern English

Early Modern English

Early Modern English is the stage of the English language used from about the end of the Middle English period to 1650. Thus, the first edition of the King James Bible and the works of William Shakespeare both belong to the late phase of Early Modern English...

 spelling for magic, used in works such as the 1651 translation of De Occulta Philosophia, Three Books of Occult Philosophy, or Of Magick. The British occultist Aleister Crowley

Aleister Crowley

Aleister Crowley , born Edward Alexander Crowley, and also known as both Frater Perdurabo and The Great Beast, was an influential English occultist, astrologer, mystic and ceremonial magician, responsible for founding the religious philosophy of Thelema. He was also successful in various other...

 chose the spelling to differentiate the occult from stage magic

Magic (illusion)

Magic is a performing art that entertains audiences by staging tricks or creating illusions of seemingly impossible or supernatural feats using natural means...

 and defined it as "the Science and Art of causing Change to occur in conformity with Will", including both "mundane" acts of will as well as ritual magic.