dick, n.² — Green’s Dictionary of Slang

dick n.²

[? link to a celebrated contemporary coachman Walter Dickson, nicknamed ‘Dickie the Driver’]

a riding whip.

1845		G.W.M. Reynolds Mysteries of London vol. 2 142: Gold-headed dick Riding whip.
1856		’The Druid’ Post and Paddock 242: A legion of Hard-Riding Dicks are ever at work.
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.
1890–1904		Farmer & Henley Sl. and Its Analogues.