Spirit is the fifth element added to the four material elements of the Greek tradition, the quintessence, literally the fifth essence, that Aristotle proposed as the incorruptible substance of the heavens, distinct from the four earthly elements of fire, air, water and earth and moving in perfect circles as they move in straight lines up or down.
In later Western esotericism this fifth element became aether or spirit, the subtle, unifying principle standing above and reconciling the other four, the source from which they proceed and to which they return. It has no single quality-pairing of the Aristotelian kind because it is held to transcend the qualities; it is associated instead with the divine, the unmanifest and the animating breath. In ritual magic spirit is the fifth point, the centre or the apex, crowning the four quarters and represented by the topmost point of the pentagram above the four elemental points. Its symbolism is of transcendence, unity and the source, the element that is not one element among others but the ground and consummation of all of them.
Sources On the Heavens (De Caelo)Aristotle with The Golden Dawn: The Original Account of the Teachings, Rites, and Ceremonies of the Hermetic Order of the Golden Dawn, 6th editionIsrael Regardie