rumble seat

English Thesaurus

1. a folding outside seat in the back of some early cars (noun.artifact)

hypernym	:	seat,
definition	:	any support where you can sit (especially the part of a chair or bench etc. on which you sit) (noun.artifact)

part meronym	:	roadster, runabout, two-seater,
definition	:	an open automobile having a front seat and a rumble seat (noun.artifact)