flatcar n freight car without permanent sides or roof Usage(s) While other carloadings were declining, there were 554,000 flatcar piggyback trips last year. General Motors' Electro-Motive Division has designed a special flatcar, 75 ft. A flatcar of lumber due for export, he reasoned, could easily be loaded in such a way that a space of two cubic yards would be left free inside. Synonym(s) flatbed flat