Dick = Richard.
The diminutive “Dicky” is also common.
“Jockey of Norfolk [Lord Howard], be not too bold,
For Dicky [or Dickon], thy master, is bought and sold.”
1
Shakespeare: Richard III., v. 3.
(Dicky or Dickon is Richard III.)
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Entry taken from Dictionary of Phrase and Fable, edited by the Rev. E. Cobham Brewer, LL.D. and revised in 1895.