rumble seat
noun
1.
Also called,
British,
dickey
. a seat recessed into the back of a coupe or roadster, covered by a hinged lid that opens to form the back of the seat when in use.
2.
Furniture.
wagon seat
.
3.
Slang.
the buttocks.
Origin
1910-15
British Dictionary definitions for
rumble seat
rumble seat
noun
1.
(
US & Canadian
) a folding outside seat at the rear of some early cars; dicky