a. the initial agent, as wind or electricity, that puts a machine in motion.
b. a machine, as a water wheel or steam engine, that receives and modifies energy as supplied by some natural source.
2. means of towing a cannon, as an animal, truck, or tractor.
3. Also called unmoved mover. Aristotelianism.that which is the first cause of all movement and does not itself move.
4. a person or thing that initiates or gives power and cohesion to something, as an idea, endeavor, or organization.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.