A rumble seat (American English), dicky seat, dickie seat or dickey seat (British English), also called a mother-in-law seat, is an upholstered exterior seat which folded into the rear of a coach, carriage, or early automobile. Depending on its configuration, it provided exposed seating for one or two passengers.
Additional occasional seating appeared in the latter centuries of evolution of the coach and carriage. The 1865 edition of Webster's An American Dictionary of the English Language defines a rumble as "A boot[note 1] with a seat above it for servants, behind a carriage." Similar to the rumble on European phaetons was the spider, a small single seat or bench on spindly supports for seating a groom or footman.
Before World War I, rumble seats did not always fold into the bodywork. Following it, such optional passenger arrangements typically were integrated into the rear deck. When unoccupied, the remaining space, if any, under the seat's lid could be used for storing luggage.
Roadster, coupe and cabriolet auto body styles were offered with either a luggage compartment or a rumble seat in the deck. Models equipped with a rumble seat were often referred to as a sport coupe or sport roadster.
Rumble seat passengers were exposed to the elements, and received little or no protection from the regular passenger compartment top. Folding tops and side curtains for rumble seats were available for some cars (including the Ford Model A) but never achieved much popularity. Among the last American-built cars with a rumble seat were the 1938 Chevrolet, the 1939 Ford and 1939 Dodge and Plymouth. The last British built car with a dickey seat was the Triumph 2000 Roadster made until 1949.