Green’s Dictionary of Slang

dicky n.4

also dickey
[East Anglian dial.; the habit of using proper names as sl. terms for donkeys]

a donkey, also attrib.

[H. Lemoine ‘The Clever Fellow’ in Wit’s Mag. 155/1: A saucy rolling blade am I, / I keep a Donkee Dick].
[UK]Lex. Balatronicum n.p.: Dickey. An ass. Roll your dickey; drive your ass.
[UK]R. Bloomfield Richard and Kate n.p.: Amongst the leaders ’twas decreed Time to begin the Dickey Races, More famed for laughter than for speed [F&H].
[UK]‘Paul Pry’ Oddities of London Life II 268: ‘As for hurting my dickey,’ said the man, ‘by lettin him fall, the gemman's werry much mistaken’.
[UK]J. Mills Old Eng. Gentleman (1847) 89: A young dickey, in the full kick of youth, mistook some sweet briar for a thistle.
[UK]Hotten Dict. of Modern Sl. etc. (2nd edn).
[UK]Hotten Sl. Dict.
[UK]Farmer & Henley Sl. and Its Analogues.