prime mover

main motive, primary motivation

The term prime mover is an English translation of the Latin Primum Mobile. The original latin refers to a "first cause" of motion in the theological sense, and was used during the scholastic era to explain how God was the cause of all movement and hence of all life in the world. It is used nowadays to describe the main power source which supports a number of subsidiary functions, commonly in industrial applications. For instance, the engine which pulls a semi-trailer is sometimes referred to as a prime mover, while a catalogue of large electric motors for powering industrial equipment might be titled 'Prime Movers'. The implication is that the 'Prime Mover' is the ultimate source of all mechanical movement in the system. As an example, in the case of an automobile, the engine is the prime mover whilst associated equipment such as the electrical generator, power steering pump, fuel pump etc. are secondary movers.
See more at Wikipedia.org...

Prime mover, n that muscle which is primarily responsible for producing a particular movement. [more]Prime mover - Community and Resources

Noun
1. a self-caused agent that is the cause of all things; "God is the first cause"
(synonym) first cause, primum mobile
(hypernym) causal agent, cause, causal agency

Synonyms and related words:
abettor, actor, actuator, agent, ancestors, animator, apprentice, architect, artificer, artist, author, begetter, beginner, builder, cajoler, catalyst, causer, coax, coaxer, conceiver, constructor, craftsman, creator, designer, deviser, discoverer, doer, effector, encourager, energizer, engenderer, engineer, executant, executor, executrix, fabricator, father, firer, founder, gadfly, galvanizer, generator, grower, impeller, inaugurator, inducer, industrialist, initiator, inspirer, instigator, institutor, introducer, inventor, journeyman, maker, manufacturer, master, master craftsman, medium, mother, mover, moving spirit, operant, operative, operator, organizer, originator, parent, past master, performer, perpetrator, persuader, planner, pleader, practitioner, precursor, primum mobile, producer, prompter, raiser, realizer, shaper, sire, smith, spark, spark plug, sparker, stimulator, subject, tempter, wheedler, worker, wright