Magick, in the broadest sense, is any act designed to cause intentional change. To change nothing into something and something into something else. (Crowley, Magick, Book 4 p.127) The spelling with the terminal "k" was repopularized in the first half of the 20th century by Aleister Crowley when he introduced it as a core component of Thelema.
"The Anglo-Saxon k in Magick, like most of Crowley's conceits, is a means of indicating the kind of magic which he performed. K is the eleventh letter of several alphabets, and eleven is the principal number of magick, because it is the number attributed to the Qliphoth - the underworld of demonic and chaotic forces that have to be conquered before magick can be performed. K has other magical implications: it corresponds to the power or shakti aspect of creative energy, for k is the ancient Egyptian khu, the magical power. Specifically, it stands for kteis (vagina), the complement to the wand (or phallus) which is used by the Magician in certain a