Thelema is the English transliteration of the Ancient Greek noun θέλημα: "will", from the verb θέλω: to will, wish, purpose. Early Christian writings use the word to refer to the will of God, the human will, and even the will of the Devil.
Thelema is also an initially fictional philosophy of life first described by François Rabelais (16th century) in his famous books, Gargantua and Pantagruel. The essence of this philosophy was summarized in the phrase "fay çe que vouldras" ("Fait çe que voudras," or, "Do what thou wilt"), and this philosophy was later put into practice in the mid 18th century by Sir Francis Dashwood at Medmenham.
This Thelemic Law of Rabelais was revived by Aleister Crowley in 1904 when Crowley wrote The Book of the Law, which contains both the word Thelema in Greek as well as the phrase "Do what thou wilt." From this, Crowley took Thelema as the name of the philosophical, mystical and religious system which he subsequently developed, which includes ideas from occultism, Yoga, and both Eastern and Western mysticism (especially the Qabalah). Thus Shri Gurudev Mahendranath, in speaking of svecchachara, a Sanskrit term which he considered the Eastern equivalent of the term Thelema, wrote that "Rabelais, Dashwood, and Crowley must share the honor of perpetuating what has been such a high ideal in most of Asia."