mid-15c., from L. motor, lit. "mover," from movere "to move" (see move). From 15c. as "controller, prime mover" (in reference to God); sense of "agent or force that produces mechanical motion" is first recorded 1660s; that of "machine that supplies motive power" is from 1856.
With explosive use 20c. as a comb. form of motor-car (1895). Motor-boat is from 1902. First record of slang motor-mouth "fast-talking person" is from 1971.