primum mobile

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The tenth and outermost concentric sphere of the universe thought in Ptolemaic astronomy to revolve around the earth from east to west in 24 hours and believed to cause the other nine spheres to revolve with it.
2. n. See prime mover.

Century Dictionary and Cyclopedia

1. n. In the Ptolemaic system of astronomy, the tenth or outermost of the revolving spheres of the universe, which was supposed to revolve from east to west in twenty-four hours, and to carry the others along with it in its motion; hence, any great or first source of motion.

Wiktionary

1. n. historical The outermost sphere of the heavens in Ptolemaic astronomy.
2. n. theology, philosophy The prime mover or first cause.

GNU Webster's 1913

1. (Astron.) In the Ptolemaic system, the outermost of the revolving concentric spheres constituting the universe, the motion of which was supposed to carry with it all the inclosed spheres with their planets in a daily revolution from east to west. See Crystalline heavens, under crystalline.

WordNet 3.0

1. n. an agent that is the cause of all things but does not itself have a cause