primum

primum mobile

[pree-moom moh-bi-le; English prahy-muhm mob-uh-lee, pree-]
Latin.
1.
(in Ptolemaic astronomy) the outermost of the 10 concentric spheres of the universe, making a complete revolution every 24 hours and causing all the others to do likewise.

Origin:
literally, first moving (thing)

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World English Dictionary
primum mobile (ˈpraɪmʊm ˈməʊbɪlɪ)
 
n
1.  a prime mover
2.  astronomy the outermost empty sphere in the Ptolemaic system that was thought to revolve around the earth from east to west in 24 hours carrying with it the inner spheres of the planets, sun, moon, and fixed stars
 
[C15: from Medieval Latin: first moving (thing)]

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Word Origin & History

primum mobile
"the first source of motion," 1460, from L. (11c.), lit. "the first movable thing;" see prime (adj.) + mobile. A translation of Ar. al-muharrik al-awwal "the first moving" (Avicenna, c.1037; Shahrastani, c.1153).
Online Etymology Dictionary, © 2010 Douglas Harper
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