Definitions of motor:

• noun:   machine that converts other forms of energy into mechanical energy and so imparts motion
• noun:   a nonspecific agent that imparts motion

  Example: "Happiness is the aim of all men and the motor of all action"

• verb:   travel or be transported in a vehicle

  Example: "They motored to London for the theater"

• adjective:   causing or able to cause motion

  Example: "Motor energy"