Source : Webster's Revised Unabridged Dictionary (1913)

Primum mobile \Pri"mum mob"i*le\ [L., first cause of motion.]
   (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}.

         The motions of the greatest persons in a government
         ought to be, as the motions of the planets, under
         primum mobile.                           --Bacon.

Source : WordNet®

primum mobile
     n : a self-caused agent that is the cause of all things; "God is
         the first cause" [syn: {first cause}, {prime mover}]