The Collaborative International Dictionary of English v.0.48:

Trailer \Trail"er\, n.
   One who, or that which, trails.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Trailer \Trail"er\, n.
   1. a wheeled vehicle without a motor, designed to be drawn by
      a motor vehicle in front of it; specifically:
      (a) such a vehicle used on street railroads. Called also
          trail car.
      (b) the large wheeled wagon or van pulled by a tractor in
          a tractor-trailer combination.
      (c) a vehicle equipped as a mobile dwelling unit, pulled
          by an automobile or other mtor vehicle, and used as a
          dwelling when parked; -- also called a mobile home.
      (d) A wheeled motorless open wagon designed to carry a
          heavy object, such as a boat trailer.
          [PJC]

   2. (Movies) A short blank segment of movie film attached to
      the end; -- used for convenient insertion of the film in a
      projector.
      [PJC]

   3. (Movies) A short film consisting primarily of one or more
      short portions of a film, used in promotions or
      advertisements shortly before initial release of a film.
      [PJC]

   4. A part of an object which extends some distance beyond the
      main body of the object; as, the trailer of a plant.
      [1913 Webster]

   trailer park. An area equipped to accommodate trailers[2],
      often with outlets supplying electrical power and water.
      Called also trailer camp, trailer court.
      [PJC]

WordNet (r) 3.0 (2006):

trailer
    n 1: someone who takes more time than necessary; someone who
         lags behind [syn: dawdler, drone, laggard, lagger,
         trailer, poke]
    2: an advertisement consisting of short scenes from a motion
       picture that will appear in the near future [syn: preview,
       prevue, trailer]
    3: a large transport conveyance designed to be pulled by a truck
       or tractor
    4: a wheeled vehicle that can be pulled by a car or truck and is
       equipped for occupancy [syn: trailer, house trailer]

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "trailer":
   3-D, Cinemascope, Cinerama, Technicolor, Western, afterpart,
   afterpiece, animated cartoon, black-and-white film, camp trailer,
   camper, caravan, cartoon, chiller, cinema, color film, creepie,
   documentary, documentary film, educational film, feature, film,
   flick, flicker, horror picture, horse opera, house trailer,
   mobile home, motion picture, motion-picture show, movie,
   moving picture, newsreel, nudie, photodrama, photoplay, picture,
   picture show, pornographic film, preview, queue, semitrailer,
   short, silent, silent film, skin flick, sneak preview,
   spaghetti Western, tab, tag, tail, tailpiece, talkie,
   talking picture, thriller, trail, trail car, trailer camp,
   trailer court, trailer park, train, truck trailer,
   underground film, wake