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
Word origin
C15: from Medieval Latin: first moving (thing)
primum mobile in American English
(ˈpraɪməm ˈmoʊbəˌli)
Latin
Astronomy
in the Ptolemaic system, the tenth and outermost concentric sphere, revolving from east to west around the earth and causing all celestial bodies to revolve with it
Word origin
ML, first movable thing: see , prime adjective & mobile