from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun 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.

from The Century Dictionary.

  • noun 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.

from the GNU version of the Collaborative International Dictionary of English.

  • (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun historical The outermost sphere of the heavens in Ptolemaic astronomy.
  • noun theology, philosophy The prime mover or first cause.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun an agent that is the cause of all things but does not itself have a cause


from The American Heritage® Dictionary of the English Language, 4th Edition

[Medieval Latin prīmum mōbile : prīmum, neuter of prīmus, first + mōbile, from neuter of mōbilis, movable (translation of Arabic al-muḥarrik al-’awwal : al-, the + muḥarrik, mover + ’awwal, first).]

from Wiktionary, Creative Commons Attribution/Share-Alike License

Post-classical Latin (from Latin prīmum neuter of prīmus ‘first’ + mōbile, from mobilis ‘mobile’), translating Arabic.


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  • "'He is the one and only primum mobile. If he were dead all his revenge and all his influence would die with him.'"

    --P. O'Brian, The Commodore, 105

    March 17, 2008