Green’s Dictionary of Slang

1. the seat in a carriage on which the driver sits.

1816		W.T. Moncrieff All at Coventry II ii: Do you mean to insinuate then, Sir, that I’m no gentleman! Zounds, don’t I [...] drive my own dicky?
1821		W. Combe Doctor Syntax, Wife (1868) 335/1: While from the dickey and the roof, / Was heard the loud and coarse reproof.
1838		Crim.-Con. Gaz. 15 Sept. 30/3: My master [...] mounted the dickey, and declared he should always drive himself.
1840		R.B. Peake Devil In London II ii: It will pop off, cork after cork, and blow me off the dickey.
1869		Glasgow Herald 11 Nov. 3/4: He was in such a helpless condition [...] that he had to be lifted on his usual perch on the ‘dickey’.
1903		A. Binstead Pitcher in Paradise 115: This idiot [...] by standing up on his dickey, managed to keep the flying pair in sight.
1906		A. McCormick Tinkler-Gypsies of Galloway 276: Jumping on to the ‘dickey,’ he accompanied them as far as the outskirts of the town.
1925		L. Mackay Mourne Folk 16: Harry, sitting on the ‘dickey,’ did not know what was up.
1994		(con. 1930s) K.C. Kearns Dublin Tenement Life 199: I was sitting up with Banker on the front, on the dickey.

2. (also dickey-box) a seat at the back of a carriage for servants etc, or of a mail-coach for the guard.

1811		Lex. Balatronicum n.p.: Dickey. [...] a seat for servants to sit behind a carriage, when their master drives.
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 67: Dickey-box — the seat at the back of a stage-coach, outside.
1823		[C.M. Westmacott] Mammon in London 1 338: [W]ithout waiting to see if Verax and Ferret were on the dicky or the box.
1832		Satirist (London) 4 Nov. 354/4: [T]he robbery must have been [...] effected during the momentary absence from the dickey of the two servants whilst lighting the carriage lamps. The leather of the hinder-box under the dickey, was cut through.
c.1850		Peeping Tom (London) 6 22/1: [I] proceeded at once in the dickey of Captain O.’s chariot.
1859		G.A. Sala Twice Round the Clock 111: Youth on the box and pleasure in the dickey.
1861		R.F. Burton City of the Saints 16: Behind, instead of [a] dicky, is a kind of boot where passengers’ boxes are stored.
1873		R. Broughton Nancy I 155: The carriage is at the door: the maid and valet are in the dickey.
1891		F.W. Carew Autobiog. of a Gipsey 335: Many a time [...] had I run after his shandrydan and hung onto the back-rail of the dickey.
1943		(con. 1880s) G.A. Little Malachi Horan Remembers 119: The guard lept down from the dickey and opened the door.

3. (also dickie) an extra seat at the back of a two-seater motorcar, which can be closed down when not in use; also of a boat.

1914		‘Bartimeus’ Naval Occasions Preface vii: ‘I reckon that’s proper “New Navy”,’ said the coxswain of a duty cutter to the midshipman perched on the ‘dickey’ seat beside him in the stern.
1920		‘Sapper’ Bulldog Drummond 37: Under the dickey seat behind lay a small bag.
1930		‘Leslie Charteris’ Enter the Saint 107: Roger tipped his police lid into the dickey and climbed into the driving seat.
1937		Jennings & Madge May the Twelfth: Mass-Observation Day-Surveys 4:46: Knock at door – surprise visit – my cousin with 5 fellow-students... pretty hefty and all came in 2-seater car with dicky.
1937		J. Worby Other Half 114: I got into the front seat [...] while the other two hobos sat at the back in the dickie seat.
1949		‘Josphine Tey’ Brat Farrar 87: ‘What about your luggage? I have just the small car but the dickey holds quite a lot’.