primum mobile (n.)

"the first source of motion," mid-15c., from Medieval Latin (11c.), literally "the first movable thing;" see prime (adj.) + mobile.

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. [Century Dictionary]

A translation of Arabic al-muharrik al-awwal "the first moving" (Avicenna). Englished by Chaucer as the firste Moeuyng (c. 1400). Old science also had primum frigidum "pure cold: an elementary substance, according to the doctrine of Parmenides."