The Collaborative International Dictionary of English v.0.48:

Motor car \Motor car\, or Motorcar \Mo"tor*car`\, n.
   1. An automobile, locomobile, or locomotive designed to run
      and be steered on a street or roadway; esp., an automobile
      specially designed for passengers and propelled by an
      internal combustion engine.

   Syn: car, auto, automobile, machine.
        [Webster 1913 Suppl.]

   2. (Elec. Railroads) Any car containing motors for
      propulsion. [U. S.]
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

motorcar
    n 1: a motor vehicle with four wheels; usually propelled by an
         internal combustion engine; "he needs a car to get to work"
         [syn: car, auto, automobile, machine, motorcar]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "motorcar":
   auto, autocar, automobile, boat, buggy, bus, car, crate, heap,
   jalopy, machine, motor, motor vehicle, motorized vehicle, tub,
   voiture, wheels, wreck