|prīməmˈmäbə(ˌ)lē noun
( plural primum mobiles )
Etymology: Middle English, from Medieval Latin, literally, first moving thing
1.
a. : the ninth or in later numbering the tenth and outermost concentric sphere added in the middle ages to the system of Ptolemaic astronomy and conceived as carrying the spheres of the fixed stars and the planets in its daily revolution — compare crystalline heaven
b. Aristotelianism : the highest physical sphere that derives its circular motion directly from God the unmoved mover
2. : something that is a first source of motion or activity : prime mover
regarded self-interest as the primum mobile of all human activity