rumble: a servant's seat (or luggage compartment) in the rear of a carriage
seat: any support where you can sit (especially the part of a chair or bench etc. on which you sit)
retrovirus: any of a group of viruses that contain two single-strand linear RNA molecules per virion and reverse transcriptase (RNA to DNA); the virus transcribes its RNA into a cDNA provirus that is then incorporated into the host cell