#trailer  a large transport conveyance designed to be pulled by a truck or tractor
  supertype:  conveyance.instrumentality__transport  something that serves as a means of transportation
  subtype:  car_carrier  semitrailer
  part of:  trailer_truck__trailertruck__tractor_trailer__trucking_rig__articulated_lorry__semi  a truck consisting of a tractor and trailer together

No statement uses or specializes trailer; click here to add one.