WordNet (r) 3.0 (2006):

boxcar
    n 1: a freight car with roof and sliding doors in the sides

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "boxcar":
   Pullman, Pullman car, baggage car, caboose, car, carriage,
   chair car, coach, coal car, covered waggon, day coach, diner,
   dinghy, dining car, drawing room, flat, flatcar, gondola, local,
   luggage van, mail car, mail van, palace car, parlor car,
   passenger car, railway car, reefer, refrigerator car, roomette,
   sleeper, smoker, smoking car, stockcar, tank, tender, truck, van,
   waggon