Wiktionary
n. (context dated English) An extra passenger seat or row of seats in an automobile, which typically folds away into a rear storage compartment.
WordNet
n. a folding outside seat in the back of some early cars
Wikipedia
A rumble seat (American English), dicky seat, dickie seat or dickey seat (British English), also called mother-in-law seat, is an upholstered exterior seat which folds into the rear deck of a two-seat pre-World War II automobile, and seats one or two passengers. When unoccupied, the space under the seat's lid could be used for storing luggage.
The 1865 edition of Webster's An American Dictionary of the English Language defines a rumble as "A boot 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.
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.
Usage examples of "rumble seat".
The seats in front and in the rumble seat were a biscuit-tan leather.
The porter piled Mason's baggage into the rumble seat, having some difficulty to find room for it.
He leaned forward from the rumble seat and thrust an envelope, a thick one, firmly sealed with scotch tape, at Galloway.
She heard his scream as he flew out of the rumble seat, and craned her head around just in time to see him caught in the metalshod fist of a Hovercraft pilot.
As I helped Laura out of the rumble seat her skirt came up and I saw those long nylon legs, the knees, the slender ankles.
Perched outside, like a rumble seat passenger in an old roadster, Austin could see Joe's head and shoulders outlined by the blue light from the control computer screen inside the watertight cockpit.
I was out front on the dirt road, trying to catch my dog, who was chasing chickens in the ditch, when he stopped his coupe, one with a rumble seat and a hand-cranked front window with gas-ration stamps on it, thirty yards down from the house.
In the rumble seat compartment of this was a portable radio transmitter-and-receiver.
The cover of the rumble seat opened slightly as though some one was peering from within, to make sure that no one was near by.
A huge wicker basket was lashed across the rumble seat with leather straps.
It contained two swarthy persons in the front buckets and another perched up on the rumble seat.
The rumble seat jumped open at his touch upon a button, and he dipped in a hand, withdrew a small box to which stout spring clamps were secured.