E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Dickey or Dicky.
A donkey; anciently called a Dick-ass, now termed Jack-ass. It is a term of endearment, as we call a pet bird a dicky-bird. The ass is called Dick-y (little Richard), Cuddy (little Cuthbert), Neddy (little Edward), Jack-ass, Moke or Mike, etc.
Dickey. The rumble behind a carriage; also a leather apron, a childs bib, and a false shirt or front. All these are from the same root. (Dutch, dekken; German, decken; Anglo-Saxon, thecan; Latin, tego, to cover.)